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United States Patent |
5,503,919
|
Litchholt
,   et al.
|
April 2, 1996
|
Garments comprising an elastomeric adhesive foam
Abstract
An elastomeric, hot-melt adhesive foam is disclosed. The adhesive foam
preferably comprises an elastomeric, hot-melt adhesive material formed
from
(a) about 15% to about 60%, by weight of the adhesive material, of an A-B-A
block copolymer, in which the A block is derived from styrene and the B
block is derived from butadiene or isoprene.
(b) about 30% to about 70%, by weight of the adhesive material, of an
aromatic modified hydrocarbon resin which associates with both the B block
and A blocks of the A-B-A block copolymer, and
(c) 0 to about 30%, by weight of the adhesive material, of a processing
oil.
The proportions of the components (a), (b), and (c) are selected such that
the elastomeric, hot-melt adhesive material has a viscosity of less than
about 200,000 centipoise at 325.degree. F. and an elastomeric retention
value of at least 75%. The adhesive material is preferably
pressure-sensitive so as to allow lamination of the solidified foam
comprising the adhesive material with components of absorbent articles
without the need for external bonding agents.
Also disclosed is a method of making the elastomeric adhesive foam and of
elasticizing structures and absorbent articles with the foam. The adhesive
foam and structures incorporating same are particularly useful in
disposable absorbent articles such as diapers, training pants, incontinent
devices, and the like.
Inventors:
|
Litchholt; John J. (Harrison, OH);
Lodge; Richard W. (Cincinnati, OH)
|
Assignee:
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The Procter & Gamble Company (Cincinnati, OH)
|
Appl. No.:
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249763 |
Filed:
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May 26, 1994 |
Current U.S. Class: |
428/101; 428/913; 442/373; 604/369 |
Intern'l Class: |
B32B /; A61M 031/00 |
Field of Search: |
428/284,286,913
604/369
|
References Cited
U.S. Patent Documents
3912665 | Oct., 1975 | Spitzer et al. | 260/2.
|
3912666 | Oct., 1975 | Spitzer et al. | 260/2.
|
4036673 | Jul., 1977 | Murphy et al. | 156/71.
|
4229548 | Oct., 1980 | Sattlegger et al. | 521/110.
|
4259220 | Mar., 1981 | Bunnelle et al. | 260/27.
|
4418123 | Nov., 1983 | Bunnelle et al. | 428/517.
|
4423161 | Dec., 1983 | Cobbs, Jr. et al. | 521/73.
|
4543099 | Sep., 1985 | Bunnelle et al. | 604/385.
|
4731066 | Mar., 1988 | Korpman | 604/366.
|
4778631 | Oct., 1988 | Cobbs, Jr. et al. | 261/128.
|
4970242 | Nov., 1990 | Lehman | 521/78.
|
4978570 | Dec., 1990 | Heyn et al. | 428/231.
|
5037416 | Aug., 1991 | Allen et al. | 604/385.
|
5056034 | Oct., 1991 | Rucki et al. | 364/510.
|
5089190 | Feb., 1992 | Trevathan et al. | 264/45.
|
5171239 | Dec., 1992 | Igaue et al. | 604/385.
|
5196000 | Mar., 1993 | Clear et al. | 604/385.
|
Foreign Patent Documents |
424295 | Apr., 1991 | EP.
| |
0526868A2 | Feb., 1993 | EP.
| |
5-123360 | May., 1993 | JP.
| |
Other References
"Handbook of Adhesives," 2d, I. Skeist (Van Nostrand Reinhold Co. 1977),
pp. 304-330.
"The Chemistry of Hot Melt Adhesives for the Nonwovens Industry;" Mark
Alper (Findley Adhesives Inc.).
|
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Henderson; Loretta J., Hersko; Bart S., Miller; Steven W.
Parent Case Text
This is a divisional of application Ser. No. 08/085,537, filed on Jun. 30,
1993 now U.S. Pat. No. 5,342,858.
Claims
What is claimed is:
1. A disposable garment comprising:
a liquid pervious topsheet;
a liquid impervious backsheet joined to said topsheet;
an absorbent core positioned between said topsheet and said backsheet; and
an elastic feature comprising an elastomeric adhesive foam positioned
between said backsheet and said topsheet; said elastomeric adhesive foam
comprising an elastomeric, hot-melt, adhesive material having cells; said
adhesive material comprising:
(a) an A-B-A block copolymer, wherein the A block is an alkenylarene
polymer and the B block is selected from the group consisting of (i) a
polymer of a 4 to 6 carbon conjugated aliphatic diene and (ii) a polymer
of a linear 2 to 6 carbon alkene;
(b) an aromatic modified hydrocarbon resin which associates with both the A
blocks and the B block of said copolymer, said resin being a single resin
vehicle selected from the group consisting of aromatic petroleum
hydrocarbon resins and hydrogenated versions of aromatic petroleum
hydrocarbon resins; and
(c) optionally a processing oil.
2. The disposable garment of claim 1 wherein the A block of said copolymer
comprises styrene and the B block of said copolymer comprises butadiene or
isoprene.
3. The disposable garment of claim 2 wherein said copolymer has a styrene
content of about 15% to about 50% of the total weight of the copolymer.
4. The disposable garment of claim 3 wherein said copolymer is
substantially fully coupled.
5. The disposable garment of claim 1 wherein said adhesive material of said
foam comprises about 15 weight % to about 60 weight % of said copolymer;
about 30 weight % to about 70 weight % of said aromatic modified
hydrocarbon resin; and up to about 30 weight % of said processing oil.
6. The disposable garment of claim 5 wherein said adhesive material
additionally comprises up to about 1 weight % of a stabilizer.
7. The disposable garment of claim 6 wherein said adhesive material
comprises:
(a) about 45 weight % of said copolymer, said copolymer being a
substantially fully coupled, styrene-isoprene-styrene block copolymer
having a styrene content of about 15% to about 50% of the total weight of
the copolymer;
(b) about 40 weight % of said aromatic modified hydrocarbon resin;
(c) about 14 weight % of said processing oil; and
(d) about 1 weight % of said stabilizer.
8. The disposable garment of claim 1 wherein said elastic feature is an
elastomeric member of an elasticized waistband.
9. The disposable garment of claim 1 wherein said elastic feature is an
elastic side panel member.
10. The disposable garment of claim 1 wherein said elastic feature is a leg
elastic.
11. A disposable garment comprising:
(i) a nonwoven coverstock having a body facing side and a garment facing
side;
(ii) a liquid impervious backsheet joined to said body facing side of said
coverstock;
(iii) an elastic feature comprising an elastomeric adhesive foam positioned
between said backsheet and said coverstock;
(iv) a liquid pervious topsheet joined to said backsheet; and
(v) an absorbent core positioned between said topsheet and said backsheet;
said elastomeric adhesive foam of said elastic feature comprising an
elastomeric, hot-melt, adhesive material having cells; said adhesive
material comprising:
(a) an A-B-A block copolymer, wherein the A block is an alkenylarene
polymer and the B block is selected from the group consisting of (i) a
polymer of a 4 to 6 carbon conjugated aliphatic diene and (ii) a polymer
of a linear 2 to 6 carbon alkene;
(b) an aromatic modified hydrocarbon resin which associates with both the A
blocks and the B block of said copolymer, said resin being a single resin
vehicle selected from the group consisting of aromatic petroleum
hydrocarbon resins and hydrogenated versions of aromatic petroleum
hydrocarbon resins; and
(c) optionally a processing oil.
12. The disposable garment of claim 11 wherein the A block of said
copolymer comprises styrene and the B block of said copolymer comprises
butadiene or isoprene.
13. The disposable garment of claim 12 wherein said copolymer has a styrene
content of about 15% to about 50% of the total weight of the copolymer.
14. The disposable garment of claim 13 wherein said copolymer is
substantially fully coupled.
15. The disposable garment of claim 14 wherein said adhesive material of
said foam comprises about 15 weight % to about 60 weight % of said
copolymer; about 30 weight % to about 70 weight % of said aromatic
modified hydrocarbon resin; and up to about 30 weight % of said processing
oil.
16. The disposable garment of claim 15 wherein said adhesive material
additionally comprises up to about 1 weight % of a stabilizer.
17. The disposable garment of claim 16 wherein said adhesive material of
said foam comprises:
(a) about 45 weight % of said copolymer, said copolymer being a
substantially fully coupled, styrene-isoprene-styrene block copolymer
having a styrene content of about 15% to about 50% of the total weight of
the copolymer;
(b) about 40 weight % of said aromatic modified hydrocarbon resin;
(c) about 14 weight % of said processing oil; and
(d) about 1 weight % of said stabilizer.
18. A disposable garment comprising:
(i) a nonwoven coverstock having a body facing side, a garment facing side,
and a liquid pervious zone;
(ii) a liquid pervious topsheet having a body facing side and a garment
facing side joined to said body facing side of said coverstock;
(iii) an elastic feature comprising an elastomeric adhesive foam having a
liquid pervious zone positioned between said coverstock; and said
topsheet;
(iv) a liquid impervious backsheet joined to said garment facing side of
said coverstock; and
(v) an absorbent core positioned between said coverstock and said
backsheet;
said liquid pervious zone of said coverstock and said elastic feature being
positioned so as to allow fluids to pass from said body facing side of
said topsheet to said absorbent core;
said elastomeric adhesive foam of said elastic feature comprising an
elastomeric, hot-melt, adhesive material having cells; said adhesive
material comprising:
(a) an A-B-A block copolymer, wherein the A block is an alkenylarene
polymer and the B block is selected from the group consisting of (i) a
polymer of a 4 to 6 carbon conjugated aliphatic diene and (ii) a polymer
of a linear 2 to 6 carbon alkene;
(b) an aromatic modified hydrocarbon resin which associates with both the A
blocks and the B block of said copolymer, said resin being a single resin
vehicle selected from the group consisting of aromatic petroleum
hydrocarbon resins and hydrogenated versions of aromatic petroleum
hydrocarbon resins; and
(c) optionally a processing oil.
19. The disposable garment of claim 18 wherein the A block of said
copolymer comprises styrene and the B block of said copolymer comprises
butadiene or isoprene.
20. The disposable garment of claim 19 wherein said copolymer has a styrene
content of about 15% to about 50% of the total weight of the copolymer.
21. The disposable garment of claim 20 wherein said copolymer is
substantially fully coupled.
22. The disposable garment of claim 21 wherein said adhesive material of
said foam comprises about 15 weight % to about 60 weight % of said
copolymer; about 30 weight % to about 70 weight % of said aromatic
modified hydrocarbon resin; and up to about 30 weight % of said processing
oil.
23. The disposable garment of claim 22 wherein said adhesive material
additionally comprises up to about 1 weight % of a stabilizer.
24. The disposable garment of claim 23 wherein said adhesive material of
said foam comprises:
(a) about 45 weight % of said copolymer, said copolymer being a
substantially fully coupled, styrene-isoprene-styrene block copolymer
having a styrene content of about 15% to about 50% of the total weight of
the copolymer;
(b) about 40 weight % of said aromatic modified hydrocarbon resin;
(c) about 14 weight % of said processing oil; and
(d) about 1 weight % of said stabilizer.
25. The disposable garment of claim 18 further comprising a second nonwoven
coverstock having a liquid pervious zone joined to said body facing side
of said topsheet, said liquid pervious zone being positioned so as to
allow fluids to pass from said body facing side of said topsheet to said
absorbent core.
Description
FIELD OF THE INVENTION
The present invention is directed to an elastomeric composition more
particularly an elastomeric adhesive foam composition. The foams are
particularly useful as an elastic component in disposable absorbent
articles such as diapers, incontinent devices, training pants, and the
like.
BACKGROUND OF THE INVENTION
Numerous absorbent articles for use in the absorption of bodily fluids and
discharges such as menses, urine, Feces and the like are known. Such
absorbent articles have incorporated elastic components to improve the fit
of the article. For example, U.S. Pat. No. 4,978,570, issued to Heyn, et
al. on Dec. 18, 1990 is directed to a disposable diaper having an elastic
waist provided with a foam strip to cushion stresses of the elastic
waistband in the waist area. The composite waistband consists of an
elastomeric strip and a foam strip. The use of a foam tends to provide
desirable properties in the article, e.g., compressibility, resilience,
and/or thickness. However, such articles suffer from the disadvantage that
the foam requires an external bonding agent to construct the article which
adds to the cost of the article. In addition, such foams generally must be
cut to fit the article as desired such that waste may be generated,
thereby further increasing the cost of the articles incorporating the
foam. Finally, foams such as the polyurethane foams disclosed therein are
prepared on a separate line for later incorporation into the article. This
need to prefabricate the foam also adds to the cost of the article.
Other prefabricated foams have been used in the art, e.g., natural rubber
foams. In addition to the disadvantages of the need to prefabricate the
foam, cut the foam to fit, and to use an external bonding agent, the
natural rubber foams are also relatively expensive.
The art also discloses elastomeric adhesive compositions which may be
combined into a laminar construction having elastic properties. For
example, U.S. Pat. No. 5,032,120, issued to Freeland, et al. on Jul. 16,
1991, discloses an improved leg cuff and a hot-melt elastomeric
composition designated 198-338 (Findley Adhesives, Inc., of Wauwatosa,
Wis.) as being particularly well suited for the construction of the
central laminate of a diaper. Other elastomeric adhesive compositions and
constructions employing same have been disclosed in U.S. Pat. Nos.
4,418,123 (Nov. 29, 1983); 4,259,220 (Mar. 31, 1981); and 4,543,099 (Sep.
24, 1985); each issued to Bunnelle, et al.
The adhesive compositions noted above possess a multiplicity of
shortcomings which have detracted from their usefulness, particularly in
disposable absorbent articles. For example, the adhesive composition
198-338 has a thin film holding strength, i.e., an elastomeric retention
when elongated, which rapidly decreases over time, thereby reducing the
usefulness of this particular adhesive composition in disposable absorbent
garments. In addition, this adhesive composition possesses an unusually
long recovery time, i.e., the time it takes for the adhesive to retract to
its original length following elongation. The elastomeric adhesive
formulations disclosed in the Bunnelle, et al., patents possess a
viscosity in excess of one million centipoise at 325.degree. F.
Consequently, these adhesive compositions can only be applied by utilizing
very expensive manufacturing machinery such as extruders and the like.
Further, this high viscosity slows the speed of production lines using
conventional manufacturing machinery, thereby increasing the manufacturing
costs of disposable garments employing these compositions. In addition,
the adhesive compositions of Bunnelle, et al. do not appear to possess the
level of adhesion which is necessary for the construction of disposable
absorbent garments. Moreover, these compositions do not appear to provide
for a convenient and expeditious means by which adhesion can be adjusted
without affecting their elastomeric properties.
U.S. Pat. No. 4,731,066, issued to Korpman on Mar. 15, 1988, discloses an
elastic laminated disposable diaper having a liquid-impermeable backing
which is produced from an initially molten extruded elastic film. The film
formers can be extruded as a foam as well as a continuous film, and
include pressure-sensitive adhesive materials. However, the
pressure-sensitive adhesives disclosed by Korpman would be expected to
possess a very high viscosity even at elevated temperatures. Consequently,
these compositions, like the compositions of the foregoing Bunnelle
patents, would be expected to require very expensive manufacturing
equipment (e.g., extruders) and to suffer from low production speeds using
conventional equipment. In addition, the structures of Korpman are limited
by the extensibility of the backing and/or facing fabric.
Thus there is a continuing need to elasticize absorbent articles in a
manner which provides the advantages of elastic components comprising
foams without the disadvantages of elastic components known heretofore.
Thus, it is an object of the present invention to provide foamed elastic
components utilizing less expensive raw materials. It is a further object
of the present invention to provide an elastomeric foam that can be formed
on-line and that does not require, or requires only reduced amounts of
external bonding agents and/or more economical bonding agents for
incorporation into absorbent articles. It is a further object of the
present invention to provide such foams which may be used to elasticize
entire panels of a disposable garment, or alternatively, discrete areas
thereof. It is a further object of the present invention to provide a
method of elasticizing absorbent articles in a direct manner without
waste. Thus it is an object of the present invention to provide a foam
which can be formed on-line in a pattern or shape. Another object of the
present invention is to provide elastic foams which may be formed into a
sheet or other shapes utilizing relatively inexpensive manufacturing
techniques or devices, and further which may be formed in a relatively
short production time. Yet another object of the present invention is to
provide foams having properties desirable for use in absorbent articles,
e.g., a relatively high elastomeric retention, a relatively short recovery
time, and good adhesion to components typically used therein.
It is a further object of the present invention to provide elastic
structures having both a low basis weight and physical properties suitable
for use in absorbent articles, e.g., a specified caliper (i.e., loft or
thickness), compressibility, resilience, and force of elongation. Yet
another object of the present invention is to provide an absorbent article
having sustained dynamic fit about the waist of the wearer and improved
resistance to leakage during use.
These and other objects of the present invention will be more readily
apparent when considered in reference to the following description and
when taken in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention relates to an elastomeric, hot-melt adhesive foam
(also referred to herein as "elastomeric adhesive foam," or "adhesive
foam") comprising an elastomeric, hot-melt adhesive material. The adhesive
material preferably comprises:
(a) about 15% to about 60%, by weight of the adhesive material, of an A-B-A
block copolymer, in which the A block (i.e., end block) is derived from
styrene and the B block (i.e., mid block) is derived from butadiene or
isoprene;
(b) about 30% to about 70%, by weight of the adhesive material, of an
aromatic modified hydrocarbon resin which associates with both the mid
block and end blocks of the A-B-A block copolymer; and
(c) 0 to about 30%, by weight of the adhesive material, of a processing
oil.
The proportions of the block copolymer, aromatic modified hydrocarbon
resin, and processing oil are preferably selected to provide an
elastomeric, hot-melt adhesive material having a viscosity of less than
about 200,000 centipoise at 325.degree. F. and an elastomeric retention
value of at least about 75%.
The invention also relates to a method of making the elastomeric adhesive
foam. The method of making the foam of the present invention involves
melting the adhesive material, mixing a gas with the adhesive material
under pressure to form a solution of the gas in the adhesive material,
reducing the pressure to cause evolution and/or expansion of the gas to
form a foam, and stabilizing the foam by causing the adhesive material to
solidify. The relatively low melt-viscosity of the adhesive material which
is used to form the foam provides desirable processing times and the
ability to form foams having desired physical properties, e.g., caliper
and cell structure.
The adhesive foams of the present invention tend to provide a desirable
elastic retention value. Thus the adhesive foams of the present invention
typically have an elastomeric retention value of at least about 65%.
Further, it is believed that, by decreasing the mount of di-block
copolymer (i.e., A-B block copolymer) in the adhesive material of the
foam, the elastomeric retention and tensile strength of the foam may be
increased. Thus, it is preferred to use block copolymers which are
substantially fully coupled, i.e.. which are substantially 100% A-B-A
block copolymer (i.e., tri-block). In a preferred embodiment, the total
concentration of styrene in the block copolymer may vary in a wide range
of from about 15% to about 50%, more preferably about 25% to about 50%, or
the total weight or the copolymer. A styrene concentration in the latter
range provides an adhesive material which displays a particularly
desirable viscosity.
The foams of the present invention are preferably pressure-sensitive. In a
preferred embodiment, the pressure-sensitive foam has a cell structure
such that the foam remains compressible upon repeated application of
compressive forces (i.e., the foam is resilient). Thus such foams are
preferably characterized by closed cells.
The present invention further relates to elastic structures and absorbent
articles incorporating the elastomeric adhesive foam, and methods of
making same. Relative to non-foamed elastomers, the foams of the present
invention tend to provide improved structural rigidity, thereby decreasing
the tendency of an absorbent article incorporating the foam to fold and/or
crease. In addition, the foams tend to provide increased resiliency and
compressibility so as to provide an improved fit of an absorbent garment
incorporating the adhesive foam. In addition, the adhesive foams tend to
distribute forces over a greater area (i.e., lower modulus), thereby
reducing the tendency for red marking and increasing the comfort of the
wearer of such absorbent articles. In a preferred embodiment, the foams of
the present invention are made on-line and integral with an absorbent
article to elasticize entire panels, or alternatively, discrete areas
(e.g., side panels) of the article.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and
distinctly claiming the invention, it is believed that the invention will
be better understood from the following drawings taken in conjunction with
the specification.
FIG. 1 is a fragmentary vertical sectional view of a laminate comprising
the elastomeric adhesive foam of the present invention;
FIG. 2 is a side elevational schematic view of one apparatus which may be
used to manufacture the laminate shown in FIG. 1;
FIG. 3 is a plan view of a disposable diaper embodiment of the present
invention having portions cut away to reveal underlying structure, the
outer surface of the diaper facing the viewer;
FIG. 4 is a fragmentary sectional view of the disposable diaper shown in
FIG. 3 taken along section line 4--4 of FIG. 3;
FIG. 5 is a fragmentary sectional view of the disposable diaper shown in
FIG. 3 taken along section line 5--5 of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The elastomeric adhesive foams of the present invention are formed from an
elastomeric, hot-melt adhesive material (also referred to herein as
"elastomeric adhesive material" or "adhesive material"). The adhesive
material is preferably pressure-sensitive.
By "elastomeric," "elastomer," "elastic," etc., it is meant materials which
are able to be stretched to at least twice their original length and to
retract very rapidly to approximately their original length when released.
"Adhesive" as used herein means a substance capable of holding materials
together by surface attachment (adhesion). Adhesion typically results from
(a) mechanical bonding and/or (b) chemical forces, including either
primary covalent bonds or polar secondary forces between the adhesive and
the surface (adherend). The particular mechanisms of bonding generally
depend on the surface characteristics, including the porosity, of the
adherend.
"Hot-melt adhesives" are those which are melted to cause flow and which are
solidified upon cooling after contacting the adherend(s), generally under
moderate pressure. Hot-melts can be characterized as solidifying by
physical processes upon cooling after being applied as a hot liquid.
"Melt," "molten," etc. as used herein includes but is not limited to the
thermodynamic melt state in which crystals of a substance are in
equilibrium with the liquid phase at a given temperature and pressure.
These terms are also meant to include an apparently homogeneous, liquid
condition. As used herein, "solidified" refers to both solid, semi-solid,
and tacky states.
As used herein, "pressure-sensitive adhesives" refers to adhesives which
are viscous polymer melts at room temperature (about 20.degree. C. to
about 25.degree. C.), which polymers are caused to flow and contact the
adherend surface by applied pressure. When the pressure is released, the
viscosity is high enough to withstand the stresses produced by the
adherends. Thus, a pressure-sensitive adhesive can be characterized as a
material which is permanently liquid but which forms a strong bond to a
surface when slight pressure is applied to cause flow of the adhesive.
An important property of a pressure-sensitive adhesive material is "tack,"
which is defined as a viscosity at room temperature which is sufficiently
low to permit good surface contact yet high enough to resist separation
under stress, typically on the order of 10.sup.4 -10.sup.6 centipoise. The
lack of pressure-sensitive adhesives can be determined by ASTM lest
methods D2979 ("Pressure Sensitive Tack of Adhesives Using an Inverted
Probe Machine") and D3121 ("Tack of Pressure-Sensitive Adhesives by
Rolling Ball"), each test being incorporated herein by reference.
By "foam," it is meant a dispersion of a gas in the molten elastomeric
adhesive material or the solidified adhesive material (the latter is also
referred to herein as a "permanent foam"). The dispersion results in a
structure which can be described as membranes or struts of adhesive
material which are interconnected so as to form cells. By "closed cell" it
is meant that a cell is completely enclosed by a membrane of the
elastomeric adhesive material. Closed cell foams are generally impermeable
by way of transport through the cells. In contrast, an "open cell" is
interconnected to at least one other cell. Typically, open cell foams are
permeable via the cellular structure.
The elastomeric, hot-melt adhesive material contains a relatively high
molecular weight hot-melt elastomer. The hot-melt elastomer is preferably
an elastomeric block copolymer having relatively non-elastomeric end
blocks and an elastomeric mid block which is designated as an A-B-A block
copolymer. A-B-A block copolymers are generally known in the art. For
example, such copolymers are described in Handbook of Adhesives, 2d Ed.,
Irving Skeist, Van Nostrand Reinhold Co. (1977), pp 304-330, incorporated
herein by reference. The A block is typically an alkenylarene polymer
derived from a monomer such as styrene. The B block is typically a polymer
of a conjugated aliphatic diene monomer of from 4 to 6 carbon atoms or a
linear alkene monomer of from 2 to 6 carbon atoms. Suitable dienes include
butadiene, isoprene, and the like. Suitable alkenes include ethylene,
butylene, propylene, and the like. Where the A block is styrene-based and
the B block is butadiene- or isoprene-based, the block copolymers are
referred to as S-B-S copolymers and S-I-S copolymers, respectively.
The block copolymers may be linear, branched or radial. In a linear
copolymer the respective monomeric moieties are arranged in an alternating
sequence such that the copolymer has the general configuration A-B-A. A
branched copolymer is essentially a linear polymer in which branching may
occur randomly anywhere in the rubber copolymer chain. A radial block
copolymer is characterized and distinguished from the branched linear
copolymer in having blocks radiating from a central core. Radial block
copolymers may be designated (A-B).sub.n X, wherein X is a polyfunctional
atom or molecule and in which each (A-B) radiates from X in a way that A
is end block ("n" refers to the number of such radiating (A-B) portions).
The preferred elastomeric adhesive material of the foam of the present
invention contains A-B-A block copolymer in an amount of about 15% to
about 60% by weight of the adhesive material. The A block is preferably
derived from styrene, alpha-methyl styrene, vinyl toluene, or mixtures
thereof. More preferably, the A block is polystyrene or a styrene based
polymer, and most preferably polystyrene. The B block is preferably
derived from butadiene or isoprene. I.e., the copolymer is preferably an
S-I-S or S-B-S copolymer.
In a preferred embodiment, the total concentration of styrene in the block
copolymer may vary in a wide range of from about 15% to about 50% of the
total weight of the copolymer. More preferably, the block copolymer has a
styrene concentration in the range of about 25% to about 50% of the total
weight of the copolymer. Such concentrations surprisingly provide adhesive
materials having particularly desirable viscosities when compared with
compounds manufactured from related A-B-A copolymers which have less than
25% styrene by weight of the copolymer.
Additionally, it has been found to be advantageous to utilize block
copolymers which are substantially fully coupled, i.e., the copolymer is
or is substantially 100% tri-block (i.e., contains low levels of or no
diblock). Preferably, the copolymer contains greater than 90% triblock,
more preferably at least about 95% triblock, even more preferably at least
about 99% triblock, most preferably about 100% triblock. It is believed
that a relationship exists between the force which is expressed as the
elastomeric retention of the adhesive material used in the present
invention and the coupling efficiency of the A-B-A block copolymer of the
adhesive material. In general, decreasing the amount or diblock tends to
increase the elastomeric retention (at a given time interval) and the
tensile strength of the adhesive material and thus of the adhesive foam.
The S-I-S and S-B-S copolymers may be a linear copolymer in which "S" is a
non-elastomeric polymeric block derived from styrene, and "I" or "B" is an
elastomeric polymeric block derived from isoprene or butadiene,
respectively. In a preferred embodiment, the total concentration of the
styrene monomer in such copolymers ranges from about 15% to about 50%,
more preferably from about 25% to about 50%, of the total weight of the
copolymer. Preferably the copolymer is substantially fully coupled.
Suitable S-I-S block copolymers of this type are commercially available
from the Dexco Chemical Company under the product or trade designations
Vector 4211, Vector 4411, and Vector 4111, respectively. Another suitable
S-I-S block copolymer is available from the Shell Chemical Company under
the trade designation RP6407. Vector 4211 and 4411 have respective styrene
contents of about 29% and 44% of the total weight of the copolymer; Vector
4111 and RP6407 each have a styrene content of about 17% of the total
weight of the copolymer.
The S-I-S and S-B-S copolymer may alternatively be a teleblock copolymer. A
teleblock copolymer includes radial copolymers characterized by molecules
having at least three branches which radially branch out from a central
hub, each of the branches having polystyrene terminal blocks and a
polyisoprene or polybutadiene segment in the center. Teleblock copolymers
also include branched copolymers having a branched polymerized isoprene or
butadiene midblock with a polystyrene terminal block at the end of each
branch. In a preferred embodiment, the total concentration of the styrene
monomer in such teleblock copolymers ranges from about 15% to about 50%,
more preferably from about 25% to about 50%, of the total weight of the
copolymer. Preferably, the teleblock copolymer is substantially fully
coupled.
Mixtures or the above-identified block copolymers may also be used. In
addition, the polymer marketed under the trade designation "Stereon"
(manufactured by the Firestone Chemical Co.) may be used herein. The
elastomeric adhesive material may also include some diblock (e.g., A-B
copolymer), although this will not generally be desired for reasons
previously stated. Thus, the adhesive material may contain diblock and/or
triblock copolymers such as are known in the art.
The elastomeric adhesive material used for preparing the foam also
comprises an aromatic modified hydrocarbon resin, preferably in an amount
of about 30% to about 70% by weight or the adhesive material. The aromatic
modified hydrocarbon resin associates with both the mid block and the end
blocks of the tri-block copolymer. Thus, the resin is chemically
compatible with both the end and mid blocks such that physical phase
separation of the polymer and the resin does not occur to a significant
extent.
The aromatic modified hydrocarbon resin tends to increase the
pressure-sensitivity (and tack) of the adhesive material and thus of the
adhesive foam, at least up to a certain level of addition relative to the
block copolymer. Up to a level of about 50% -60% resin, the adhesive
material tends to increase in pressure-sensitivity with an increase in
resin. Above about 60% resin, the adhesive tends to decrease in
pressure-sensitivity and may become relatively hard and glassy. In
addition, as the pressure-sensitivity increases, the elastomeric retention
of the adhesive material tends to decrease until the glassy phase is
reached. Similarly, the tensile strength of the adhesive material and foam
may decrease with increasing levels of resin relative to the copolymer, at
least until the adhesive material becomes glassy. The aromatic modified
hydrocarbon resin also tends to decrease the viscosity of the adhesive
materials
The aromatic modified hydrocarbon resin may be selected from the group
consisting of aromatic petroleum hydrocarbon resins and hydrogenated
versions thereof. Particularly suitable resins of this type are
commercially available from the Exxon Chemical Company under the trade
designation "ECR 165A" and "ECR 165C." Other aromatic modified hydrocarbon
resins are styrenated terpenes, such as those materials which are marketed
under the trade designation "Zonatac 105 Lite" (manufactured by the
Arizona Chemical Company).
The elastomeric adhesive material also preferably comprises a processing
oil. Preferably, the oil is present in amounts of up to about 30% by
weight of the adhesive material. The oil provides some level of viscosity
control and further operates as a diluent. The viscosity of the adhesive
material tends to decrease as the amount of processing oil is increased.
In addition, the processing oil tends to contribute to the
pressure-sensitivity (and tack) of the adhesive material and foam.
However, increasing levels of oil also tend to decrease the elastomeric
retention and tensile strength of the adhesive material and foam.
The oil is preferably compatible with the other components of the adhesive
material such that a homogeneous mixture is formed, i.e, the mixture does
not phase separate to a significant extent. In a preferred embodiment, a
paraffinic or napthenic white processing oil such as are known in the art
is used. A commercially available white processing oil suitable for use
herein is available from the Witco Chemical Company as "Witco Plastics Oil
380." Another suitable oil is "Kaydol," which is also available from the
Witco Chemical Company.
In a preferred embodiment, the proportions of the block copolymer, aromatic
modified hydrocarbon resin, and processing oil are selected to such that
the adhesive material of which the adhesive foam is comprised has a
viscosity of less than about 200,000 centipoise at 325.degree. F. and an
elastomeric retention of at least about 75%. In another embodiment, the
adhesive material preferably also has a tensile strength of at least about
5 psi at 40% elongation at 25.degree. C. The proportions can be selected
in accordance with the pervious description of the foregoing components.
It is further noted that the elastomeric retention and tensile strength
tend to increase with increasing levels of the copolymer.
The proportions of the block copolymer, aromatic modified hydrocarbon
resin, and processing oil are also preferably selected in accordance with
the foregoing description such that the adhesive material is
pressure-sensitive (thus, the adhesive material has tack).
Pressure-sensitivity may advantageously allow for the elasticization of
absorbent articles without the need for external bonding agents, depending
on the level of adhesion to a given substrate.
It may be desirable to balance the pressure-sensitivity of the adhesive
material with the cell structure in order to provide a resilient foam. It
is believed that, the higher the tack, the greater the tendency of the
foam to lose compressibility, resulting in reduced caliper and a change in
other physical properties. It is believed that the tack may be sufficient
to cause open cell walls to cohere upon compression of the foam, resulting
in a change in cell structure and a consequent loss of compressibility and
other physical properties. It is further believed that this tendency can
be offset by varying the open/closed cell ratio (the percent of open
cells: the percent or closed cells; hereinafter referred to as the "cell
ratio") of the elastomeric adhesive foam. In general, for a given
elastomeric adhesive material, tile smaller the cell ratio (i.e., the
greater the number of closed cells relative to open cells), the less the
tendency of the foam to lose compressibility. The greater the tack, the
more desirable it will usually be to have a substantially closed cell
structure. Modification of the cell ratio is further described herein.
The elastomeric adhesive material of which the adhesive foam is comprised
also preferably comprises a compound which functions as an antioxidant
and/or thermal stabilizer (hereinafter referred to as stabilizer). The
stabilizer tends to protect the block copolymer, and thereby the adhesive
material and adhesive foam incorporating same, from the deleterious
thermal and/or oxidative effects which are frequently experienced by other
similar copolymers during the manufacture and application of adhesive
compositions utilizing same, as well as in the ordinary use of the final
manufactured product. As should be understood, such degradation usually
manifests itself by the deterioration of the adhesive material in
appearance, physical properties and performance.
Particularly useful stabilizers for use herein include the high molecular
weight hindered phenols and multi-functional phenols, such as sulfur and
phosphorous-containing phenols. The hindered phenols are well known to
those skilled in the art. Exemplary stabilizers of this type may be
purchased commercially under the trade designation "Irganox 1010" from the
Ciba-Geigy Company. Other useful stabilizers include "Cyanox LTDP,"
manufactured by American Cyanamid, and "Mark 273," manufactured by the
Wilco Chemical Company. The performance of these stabilizers may be
enhanced by utilizing in conjunction therewith: (1) synergists, e.g.,
thiodipropionate esters and phosphites; and/or (2) chelating agents and
metal deactivators, e.g., ethylenediamineletraacetic acid (EDTA), salts of
EDTA, and di-salicylapropylene-di-imine. The stabilizer is typically used
in an amount of less than about 5% by weight of the copolymer, preferably
less than about 2% by weight of the copolymer, more preferably less than
about 1% by weight of the copolymer.
In a preferred embodiment, a nucleating agent is incorporated into the
elastomeric adhesive material. The nucleating agent tends to increase the
foam growth rate and also influences the size distribution of the
resultant bubbles. It is generally desirable to minimize the foam growth
time (i.e., to increase the foam growth rate) in order to enable
processing on conventional converting equipment such as used in the
manufacture of disposable absorbent articles. The foam growth rate refers
to the rate of change of volume of the foam (e.g., due to gas evolution
and/or expansion out of or in the gas/adhesive material solution described
herein); the foam growth time refers to the time required to achieve about
99% of final caliper once the solution is dispensed. For a given diffusion
condition, the foam growth time lends to decrease with a decrease in
viscosity. Thus, the growth time tends to decrease with an increase in
temperature and/or with compositional variations as described herein
(although the utility of such temperature increases is limited by the
decomposition temperature or the adhesive material). The foam growth time
is typically less than about 2 seconds, depending on the process
temperature. For one system, the foam growth time was about 0.5 seconds.
In the absence or a nucleating agent, the gas/adhesive material solution
will typically need to be supersaturated in order to drive the gas
evolution to a degree sufficient to form a foam. Nucleation or gas bubbles
may then occur according to known principles, e.g., due to surface
imperfections in the apparatus used to form the foam. Such nucleation is
expected to result, however, in random bubble formation. Any bubbles which
so form tend to be larger in size and fewer in number than when a
nucleating agent is used. In addition, the foam growth time tends to to be
somewhat slower than when a nucleating agent is used.
The nucleating agent tends to indirectly increase the foam growth rate.
Generally, when a nucleating agent is used, the bubbles will immediately
form and begin to grow when the pressure of the system has been reduced to
at least the critical solubility pressure, defined herein. It is believed
that the growth involves both diffusion of dissolved gas molecules toward
a gas phase in the bubbles and expansion of the gas bubbles. It is also
believed that the nucleating agent in sufficient quantity decreases the
mean diffusion path between gas bubbles since the agent induces a greater
concentration of bubbles in the solution, thereby increasing the rate of
gas diffusion out of solution (evolution) upon a sufficient decrease in
pressure. As a result, the foam growth rate is increased.
The rate of diffusion and thus of foam growth may also be increased by a
decrease in viscosity of the gas/adhesive solution. A decrease in
viscosity also tends to increase the foam growth rate by decreasing the
flow resistance of adhesive melt surrounding the gas bubbles, thereby
enhancing expansion of the gas bubbles. Expansion of the bubbles is
believed to occur until the internal pressure of the bubbles is balanced
by the surface tension of the bubble in the solution. A decrease in
viscosity and resultant increase in foam growth rate may be achieved by
increasing the temperature of the gas/adhesive solution and through
compositional variations as previously described.
The nucleating agent also tends to increase the modulus of the adhesive
foam. It is believed that the nucleating agent tends to provide a
relatively monodisperse cell distribution resulting in a higher modulus
foam. Use of a nucleating agent typically results in a foam having a
greater number of cells, which cells will be of a smaller size, relative
to foams comprising adhesive material in which no nucleating agent is
used. For a given amount of nucleating agent and gas, the smaller the
particle size of the nucleating agent (i.e., the greater the number of
nucleating agent particles), the greater the number of resultant gas
bubbles and cells, the more uniform the cell structure, and the fewer the
number or defects (e.g., random large cells having relatively thin, weak
cell walls).
Nucleating agents such as are known in the art, e.g., CaCO.sub.3 and
TiO.sub.2, may be used. The Nucleating agent is typically used in an
amount of about 0.5% to about 1% by weight of the adhesive material. The
specific nucleating agent level will generally be balanced with the effect
of the agent on the viscosity of the adhesive material. The viscosity of
the adhesive material tends to increase with increasing levels of the
nucleating agent.
The elastomeric adhesive material from which the foam of the present
invention is made may be prepared using any of the techniques known in the
art for conventional elastomeric adhesives. For example, the oil and
stabilizer components, when used, may be placed in a jacketed mixing
kettle, preferably a jacketed heavy duty mixer of the Baker-Perkins or Day
type which is equipped with rotors. Thereafter, the temperature of the
mixture is raised to a temperature sufficient to melt the various adhesive
components, typically about 250.degree. F. to about 350.degree. F. As
should be understood, the precise temperature to be used in this step will
depend on the melt point of the particular ingredients. After this initial
mixture has been healed to the desired temperature, the mixture is
blanketed in a non-reactive gas, e.g., CO.sub.2, at a slow flow rate, and
the aromatic modified hydrocarbon resin is slowly added. When the resin is
melted, the block copolymer is added to the mixture. The resultant
adhesive composition is agitated thereafter until the block copolymer is
completely melted. The temperature may be increased to melt the copolymer;
typically a temperature in the range of about 250.degree. F. to about
350.degree. F. is sufficient. A vacuum may be applied to remove any
entrapped air. The elastomeric adhesive material may then be recovered for
later use in making the foam of the present invention. Alternatively, the
mixing kettle used to make the adhesive material is connected to equipment
for making the foam so as to enable a continuous process.
The foams of the present invention are generally formed by first melting
the elastomeric adhesive material. The adhesive is typically melted by
heating to a temperature of about 250.degree. F. to about 400.degree. F.,
preferably about 325.degree. F. to about 375.degree. F. Generally the
temperature will be maximized in order to increase the flow rate of the
material, however, the temperature and the time held at the temperature
should be selected so as to avoid polymer degradation. The molten
elastomeric adhesive material is then mixed under sufficient pressure with
a suitable gas to form a solution of the gas in the elastomeric adhesive
material (a foamable composition is formed). Upon a sufficient reduction
in pressure, the gas evolves from and/or expands in the solution in the
form of bubbles in the molten adhesive material to form a structure
comprising the elastic adhesive material and cells (a foam is formed). The
structure is stabilized, e.g., by cooling the adhesive material, to form a
foam structure which is relatively permanent at room temperature.
The gas is preferably non-reactive, i.e., it is non-oxidative or does not
promote oxidation. Thus various gases may be employed in the present
invention, including nitrogen, carbon dioxide, inert gases such as argon
or helium, and mixtures of any of the foregoing gases. Although oxidative
gases such as air may be used, this is not preferred and would usually
require the use of a stabilizer and/or steps to dry the air in order to
prevent or minimize oxidation of the elastomeric adhesive material.
Preferably, a non-reactive gas is selected which has substantial
solubility in the adhesive material at the temperature and pressure
employed. Preferably, nitrogen is used.
It is often desired to minimize the foam density and thus to maximize the
amount of gas in the solution for economic and other reasons, e.g., to
maximize caliper. Thus, the amount of the gas which is incorporated into
the molten elastomeric adhesive material may be selected so as to provide
a foam having a desired density or caliper. However, since the foam
modulus tends to decrease with decreasing foam density (and thus with
increasing gas loading) the desired density should be balanced with the
desired modulus. Typically, at least about 25 volume %, more preferably at
least about 50 volume % of gas is incorporated into the elastic adhesive
material. About 65 volume % to about 75 volume % gas tends to provide a
suitable balance of foam density, caliper, and modulus. The resultant
foams typically have, respectively, a void volume of at least about
20-about 25%, at least about 40-about 50%, about 50-about 65%; and about
60-about 75%.
The term "solution" is used herein to describe the molten elastomeric
adhesive containing the gas supplied under a pressure above atmospheric
pressure and sufficient to cause the gas to rapidly evolve and/or expand
when the pressure is reduced to atmospheric pressure such that a foam is
formed. The solution is a relatively homogeneous mixture of the gas and
molten adhesive material, the gas molecules being dissolved and/or
dispersed in the adhesive material.
The pressure under which the adhesive material and gas is maintained to
form the solution is preferably at least as great as the critical
solubility pressure of the particular gas in the elastic adhesive
composition at a given temperature. As used herein, "critical solubility
pressure" means the pressure at which the gas in solution will begin to
evolve out of the solution. The critical solubility pressure is typically
the same as or near to the thermodynamic equilibrium solubility pressure.
In addition, the critical solubility pressure tends to follow Henry's law,
i.e., the weight (or volume) of the gas dissolved in a given amount of the
adhesive material is directly proportional to the pressure exerted by the
gas when in equilibrium with the solution. Thus, the critical solubility
pressure may be determined for a given gas loading and adhesive material
in the following manner. It has been found that the critical solubility
pressure (P.sub.cs) is equal to a coefficient (A) multiplied by x/(1-x)!,
where "x" is the gas volume fraction of gas added to the adhesive
material, at standard temperature and pressure. (A) can be determined from
a plot of P.sub.cs against x/(1-x)!, (A) being the slope of the resultant
line. P.sub.cs is determined for at least two gas volume percentages by
injecting a known volume percent of gas at standard temperature and
pressure into a known quantity of adhesive material under a pressure such
that, after sufficient mixing and time, no gas bubbles are visible. The
pressure is then reduced until bubbles appear and further until the point
at which the bubbles begin to grow in size. The pressure at which initial
enlargement is apparent to the naked eye is taken as the critical
solubility pressure P.sub.cs. The critical solubility pressure for a
desired gas loading is then determined by multiplying the coefficient (A)
by x/(1-x)! where "x" is the desired volume fraction of the gas.
Additional pressure above the critical solubility pressure will generally
be necessary in order to form and transport the solution within the
residence times and mixing regimes typical of commercial foaming
equipment. The total pressure is referred to herein as the "solubility
pressure." Typically, for nitrogen gas, the solubility pressure is
approximately twice the critical solubility pressure. For example, for a
gas volume fraction of 85%, 1600 psi is used for a gas/adhesive material
solution with a critical solubility pressure of 750 psi.
Upon a sufficient reduction in pressure, the gas evolves from and/or
expands in the solution in the form of bubbles in the molten adhesive
material to form a structure comprising the elastic adhesive material and
cells (a foam is formed). The solution is typically caused to foam by
decreasing the pressure to a point below the critical solubility pressure.
It is typically desired to avoid the reduction of pressure until tile
desired point of discharge. If the critical solubility pressure is reached
before this point, there may be a loss of gas resulting in a decreased
caliper. It is believed that, if the critical solubility pressure is
reached before discharge, the wall shear exerted by a typical fluid
transport system causes the bubbles flowing near the walls of the
dispensing device to elongate and weaken. As a result, bubbles can burst
upon exiting the device such that gas is lost and there is a decrease in
caliper and an increase in density (and basis weight). An increased number
of open cells relative to closed cells may also result.
A particularly suitable method of incorporating the gas into the adhesive
material utilizes the FoamMix.RTM. system available from the Nordson
Corporation of West Lake, Ohio. This system is described in detail in U.S.
Pat. Nos. 4,778,631, issued to Cobbs, Jr. et al., on Oct. 18, 1988; and
5,056,034, issued to Rucki, et al. on Oct. 8, 1991. With such a system,
the adhesive material may be mixed with the gas to provide an adhesive/gas
solution under pressure such that when the adhesive/gas solution is
subsequently discharged at atmospheric pressure, the gas is released from
the solution and becomes entrapped in the adhesive material to form a
relatively homogeneous foam. In the FoamMix.RTM. system, mixing is
accomplished by force feeding the gas and adhesive material into and
through a low energy input disc mixer with a low pressure drop across the
mixer such that premature foaming of the adhesive material is prevented or
minimized. The disc mixer includes a tubular housing, one or more drive
shafts extending along the length of the housing, and a series of discs
spaced along the shafts. The gas enters into solution with the copolymer
mixture in the compartments between the rotating discs. The overall
pressure drop of the system is kept sufficiently low relative to the
temperature increase of the material to maintain the gas in solution
throughout the system and up to the dispensing device, e.g., a valved
nozzle, to avoid foaming of the material prior to discharge. A sufficient
pressure differential across the dispensing device is provided to maintain
the gas in solution prior to discharge, yet to permit foaming after
discharge at atmospheric pressure.
Another system suitable for forming and dispensing the foamable composition
is the FoamMelt.RTM. system available from the Nordson Corp. This system
is described in U.S. Pat. No. 4,679,710, issued to Jameson et al. on Jul.
14, 1987, incorporated herein by reference.
The foam is stabilized by cooling the molten adhesive material. Under
laboratory conditions, ambient temperatures will generally suffice.
Alternatively, the cellular structure may be cooled by external means,
e.g., chill rolls. It is generally desired to immediately form a skin on
the foam suffices by cooling just the outside surfaces in order to prevent
or minimize gas loss. Generally, every chilled suffice will form a skin
thereon. However, sufficient time should be allowed for the gas bubbles to
grow to substantially their maximum size at standard temperature and
pressure (i.e., the gas is at or near its equilibrium pressure at standard
temperature and pressure). If the adhesive material sets prior to such
growth, there may later be an apparent gas loss resulting from the
pressure exerted by the gas entrapped in closed cells. It is believed that
this pressure may be sufficient to cause diffusion of the gas out of the
foam structure such that the cellular structure and physical properties of
the foam change over time. Typically, sufficient time is provided by
allowing at least about 0.5 second, preferably about 2 seconds, before
cooling and any compression.
In addition, it is usually desired to form and stabilize the foam structure
in the substantial absence of compressive forces (e.g., compression or
tension). Such forces may limit the growth of the gas bubbles resulting in
reduced caliper and a change in other physical properties. For example,
tensioning rolls and combining rolls such as are typically used in
commercial laminating equipment may cause compressive forces. Therefore,
lamination preferably occurs after the foam structure has solidified
(e.g., using the pressure-sensitive properties of the adhesive material of
the foam and/or external bonding agents as described herein). Lamination
may alternatively occur before cooling (i.e., via the hot-melt properties
of the adhesive material if the process is carefully engineered to avoid
compression during solidification. For example, the clearance of the
combining rolls may be set to the loft of the unsolidified foam existing
at the time the laminae pass through the combining rolls.
The gas/adhesive material solution is typically applied to a substrate upon
which foaming is desired to occur. Suitable substrates include permanent
substrates (i.e., the elastomeric adhesive foam will be used as an
integral pan of the substrate such that the substrate is a carrier as
further described herein) and temporary substrates (e g., release paper,
transfer webs and molds). A foam formed on a temporary substrate is later
suitably affixed to a carrier. The solution may be applied to the
substrate by any suitable method for preparing films, for example, casting
and slot coating. The solution can be applied to the substrate to obtain a
foam product in a desired shape, and/or in any discontinuous or continuous
pattern.
The foam is typically shaped during and/or after its formation. Shaping may
be achieved by any conventional shaping technique as are known in the art
to form a foam having a defined shape and size. Preferred methods for
shaping the foam include casting molding, or forming operations. Casting
and molding techniques generally involve introducing the solution into a
prepared mold cavity or onto a substrate and reducing the pressure such
that the foam expands into the shape of the mold cavity or substrate.
Examples of specific molding techniques for use herein include injection
molding, rotary molding, and vacuum molding. Forming techniques involve
performing various operations on the gas/adhesive material solution or
foam to modify its shape and/or size. Examples of specific forming
techniques for use herein include coating, extruding, and laminating
operations. For example, the solution may be dispensed through an orifice
to form a foam having a shape corresponding to the shape of the orifice.
In addition, the foam shape can be controlled by using an intermittent
nozzle or a row of intermittent nozzles of a variety of shapes (e.g., slot
or bead). By turning selected nozzles on and off over the substrate
passing below, a multitude of two-dimensional patterns or shapes can be
made. Further, the solution may be east on a surface to form a foam having
a desired shape or surface morphology. Any or all of these techniques may
also be used in combination to form the shaped foam. Any suitable
apparatus as are known in the art may be used to carry out such
operations.
The resultant elastomeric adhesive material foam in an uncompressed state
can be described as a relatively homogeneous dispersion of a gas in the
elastomeric adhesive material. The gas can be dispersed to form closed
and/or open cells, as previously defined. The foam may thus be
characterized by a cell ratio, i.e, the percent open cells/percent closed
cells. The cell ratio and other features can impact on various properties
of the foam, including caliper, elongation force, compressibility, and
resilience.
The cell ratio may be varied by changing the percent of gas incorporated
into the elastomeric adhesive material. The cell ratio may also vary with
the viscosity, and thus the temperature, of the gas/adhesive material
solution. For a given viscosity and temperature, the cell ratio tends to
increase with an increase in gas loading (volume % or fraction). For a
given gas loading, the greater the viscosity or the lower the temperature,
the greater the tendency for closed cells to form such that the cell ratio
decreases. Without wishing to be bound by theory, it is believed that a
gas loading of about 50 volume % provides at least about 90% closed cells
(cell ratio of 1:9) at the process temperatures typically used, e.g.,
325.degree. F. Gas loadings of 75-80 volume % may provide up to about 75%
closed cells (cell ratio 4:3), depending on the process temperature used.
The cell ratio may also be influenced by the length of the time period
between the point at which the critical solubility pressure is reached and
the point of discharge of the solution from, e.g., a dispensing nozzle
(i.e., the "transit time"). It is believed that the longer the transit
time, the more likely the formation of open cells and consequent gas loss
and reduced caliper (it is believed that open cells tend to form as a
result of wall shear during transport). For example, one system displayed
about 50% gas loss for a transit time of about 10 milliseconds. Thus, the
shorter the transit time, the lower the cell ratio tends to be.
The transit time tends to decrease with an increase in the flow rate of the
solution in a transport system. Thus, any factor tending to increase the
flow rate tends to decrease the transit time and the cell ratio. For
example, the transit time may be reduced by decreasing the viscosity,
e.g., by increasing the temperature, of the solution. The transit time may
also be reduced by decreasing the length of the transport system, e.g.,
the dispensing device (e.g., nozzle).
For use in absorbent articles, it is generally preferred that the foam have
a caliper of from about 25 to about 60 mils, preferably from about 35 to
about 45 mils. Foams having such calipers are believed to aid in providing
sufficient stiffness to prevent or minimize rolling and/or creasing of
structures incorporating the foam. In addition, these calipers provide a
desirable aesthetic effect in articles incorporating same.
Features influencing caliper include the gas loading, temperature, line
speed, basis weight, tack, and cell ratio. With the other features
constant, caliper tends to increase with increasing gas loadings and to
decrease with increasing line speed. In addition, as the adhesive tack
increases, the foam caliper may tend to decrease after compression of the
foam. This effect is more likely as the cell ratio increases. Thus,
suitable foams may require using lower process temperatures and/or reduced
transit times in order to ensure a percentage or closed cells sufficient
to retain an initial caliper (and compressibility) after the foam is
subjected to compressive forces, e.g., during processing or in use.
Caliper is also affected by the ability of the foam to grow. In general,
if the foam has not been allowed to grow prior to solidification, less
than theoretical caliper (based on gas loading and line speed) will
result. As previously described, foam growth tends to be maximized by
ensuring adequate time for the gas to expand and by minimizing compressive
forces prior to solidification.
The foams of the present invention may also be characterized by a force of
elongation at 50% extension as defined herein in reference to elasticized
side panels of absorbent articles. The force of elongation is primarily
determined by the elastomeric adhesive material making up the foam. The
force of elongation is also influenced by the foam density. For a given
cell ratio and cell size, the force of elongation tends to increase with
an increase in foam density (i.e., with a decrease in gas fraction). The
force of elongation of the foam may also be influenced by the cell ratio.
The elongation force lends to increase as the cell ratio decreases. Thus,
the elongation force may be increased by any of the methods of decreasing
the cell ratio, e.g., decreasing temperature or gas loading.
The foams of the present invention are also compressible. By compressible,
it is meant that the foam can be pressed down by a fairly low force, e.g.,
1 psi. The foams are also resilient, i.e., they relax back substantially
to their pre-compressed state upon removal of the compressive force.
Compressibility and resilience are primarily a result of the foam cellular
structure and the elastomeric properties of the elastomeric adhesive
material. Thus, any factor which influences the cell structure and
elastomeric properties may impact on compressibility and resilience. In
general, compressibility tends to increase as the cell ratio increases
(increasing open cells) while resilience tends to increase as the cell
ratio decreases (increasing closed cells). For a given cell ratio, both
compressibility and resilience tend to decrease with increasing adhesive
tack.
The percent compression and resilience of the adhesive foams can be
determined by standard methods. A piece of the foam with a predetermined
caliper is compressed by a force of 1 psi in the direction of the measured
caliper for a period of 1 minute. The force is then removed and the foam
is allowed to relax for 2 minutes. The caliper under compression at 1
minute and the caliper after relaxation are determined. The percent
compression is calculated as: (initial caliper-caliper under
compression)/(initial caliper),.times.100!. The percent resilience is
calculated as: (caliper after relaxation)/(initial caliper),.times.100!.
The foams of the present invention preferably have a percent compression
of at least about 5%, more preferably at least about 20%. The foams
preferably have a percent resilience of at least about 90%, more
preferably about 100% .
The foams of the present invention are useful when joined to a carrier, and
are particularly useful for imparting elastomeric properties to the
carrier. The carder may be any carrier as are known in the art such as
non-woven webs, apertured polymeric webs, and polymer films. Suitable
carriers include any of the top sheet, back sheet, or absorbent core
materials described herein for use in absorbent articles. The carrier may
be of any desired shape and may be shaped before, during or after joinder
with the foam.
The foam is preferably joined to the carrier via the adhesive properties of
the elastomeric adhesive material making up the foam. For relatively low
tack foams, external bonding agents such as those adhesives described
herein in reference to joinder of the backsheet may be desired. The foam
may be joined to the carrier in a continuous process, i.e. on-line, or
after forming the foam in an intermediate step, i.e., off-line The foam
may be joined to one or more carriers, e.g., to form a bilaminate or a
trilaminate in which the foam is the central lamina and two carriers are
the outboard laminae.
In a continuous process, the foam may be joined to at least one carrier via
the hot-melt and/or pressure-sensitive properties of the adhesive foam.
External bonding agents may also be used to effect or enhance joinder. In
a preferred embodiment, joinder occurs via the hot-melt and/or
pressure-sensitive properties of the elastomeric adhesive material of
which the foam is comprised.
Joinder via the hot-melt property of the adhesive material to at least one
carrier occurs where the foam is formed directly on a permanent substrate,
e.g., a backsheet material for use in absorbent articles. For formation of
a laminate via the hot-melt property of the adhesive material, it is
desirable to provide sufficient contact of the carrier(s) with the
hot-melt in order to ensure bonding, without subjecting the laminate to
compressive forces which undesirably limit foam growth. The temperature of
the hot-melt may need to be regulated in order to avoid or minimize
deformation or melting of the carrier(s). A trilaminate can also be formed
by solidifying the foam on a first carrier (the resultant bilaminate is
via the hot-melt property) followed by joinder of a second carrier via the
pressure-sensitive properties of the adhesive material and/or an external
bonding agent where the adhesive foam has relatively low adhesion to the
second carrier. In a preferred embodiment, the foam has sufficient tack so
as to allow joinder to the second carrier via the pressure-sensitive
property of the foam.
In another continuous process, the foam is formed and solidified on a
temporary substrate such as a forming roll or forming belt (e g., a
transfer belt) and then affixed to one or more carriers via the
pressure-sensitive property of the foam and/or an external bonding agent.
Preferably, a foam having sufficient pressure-sensitivity to allow joinder
without additional bonding agents is used. The forming roll may be smooth
to provide a continuous sheet of the foam, or patterned (e.g., a rotary
mold such as a "pocket" or "pattern" roll, and preferably using at least
one intermittent dispensing device) to provide foam shapes as may be
desired. The forming roll will preferably be selectively chillable, e.g.,
the roll will be capable of rotating the solution and/or foam from between
non-chilled and chilled zones. In a preferred embodiment, the gas/adhesive
material solution is dispensed onto a non-chilled zone, allowed to foam,
and then rotated to solidify the foam structure. Foam shapes may
alternatively be formed by using at least one intermittent dispensing
device and a smooth forming roll or forming belt. The shaped foam may then
be affixed to a carrier, for example, directly off of the roll or after
intermediate transfer to a transfer web.
In an off-line process, the foam is directly formed on a temporary
substrate such as release paper. After solidification of the foam
structure, the foam can be joined to one or more carriers via the
pressure-sensitive adhesive properties of the foam and/or an external
bonding agent.
Where the foam is solidified prior to joinder to one or more carriers, it
may be applied to a first carrier in a pre-stretched (i.e., contractible)
condition or in a non-stretched condition. If applied in a stretched
condition, the stretch of the resultant bilaminate will generally be
maintained through the step of joinder to a second carrier where a
trilaminate is desired.
As shown in FIG. 1, the elastomeric adhesive foam can be joined to two
carriers to form a unitary, elastically extensible laminate 30 having at
least three laminae. The central lamina 30b comprises the adhesive foam of
the present invention, and is joined in face-to-face relation with at
least two outboard laminae 30a and 30c. The outboard laminae may be any of
the materials described herein in reference to the carrier, and typically
comprise a relatively inextensible material.
Referring to FIG. 2, the laminate 30 of the present invention may be
produced on the illustrated apparatus 310. The apparatus 310 comprises
three separate lines: line 312b for the central lamina 30b and
complimentary lines 312a and 312c for the outboard laminae 30a and 30c.
The first line 312b, utilized for the central lamina 30b, comprises a
source of the foamable gas/adhesive material solution (not shown), a
dispensing device 316 and a chill roll 318 to form the web of the central
lamina 30b. The outboard laminae 30a and 30c are formed on lines 312a and
312c. The materials used for the outboard laminae 30a and 30c are taken
from unwind rolls 326a and 326c through S-wrap tensioning rolls 328a and
328c and, if desired, through tracking systems 314a and 314c. The
combining rolls 324 join the confluent laminae 30a, 30b, and 30c into a
unitary laminate 30.
Examining FIG. 2 in more detail, the apparatus 310 comprises the means for
joining at least three laminae in face-to-face relation. The central
lamina 30b is formed from a supply of foamable gas/adhesive material
solution (not shown). The source of the foamable solution is suitably the
mixer of the FoamMix.RTM. system shown in the above referenced patents to
Cobbs, Jr., et al. and Rucki, et al. The foamable gas/adhesive material
solution is generally held at a temperature of about 325.degree.
F.-375.degree. F. and a pressure of about 500-2,000 psig.
The mixer supplies the foamable solution, under pressure, to the dispensing
device 316. The dispensing device 316 may be, for example, the nozzle
shown in FIG. 1 of the above referenced U.S. Pat. No. 4,778,631 issued to
Cobbs, Jr., or the gun 26 as shown in FIG. 1 of the above referenced U.S.
Pat. No. 5,056,034 issued to Rucki, et al. The dispensing device 316 has a
slot through which the foamable solution for forming the central lamina
30b is dispensed to form a thin film of foam (typically about 5-15 mils in
thickness unfoamed, 20-60 mils in thickness foamed) and of any desired
width, onto the chill roll 318. A central lamina 30b of about 0.05-0.2
grams per square centimeter is suitable. It will be apparent to one
skilled in the art that increasing the thickness of the lamina 30b will
provide a proportional increase in the ultimate elastic strength of the
lamina 30b and thus the laminate 30.
Upon discharge of the solution to atmospheric pressure, the foam forms as
previously described. The chill roll 318 preferably cools the lamina 30b
to prevent damage to the carrier but without hindering foam growth. The
web of the central lamina 30b is separated from the chill roll by a doctor
blade 320. A second roll (not shown) may be utilized in conjunction with
the chill roll 318 to provide additional cooling to solidify the laminate
and a nip for compression of the web of the central lamina 30b.
The central lamina 30b is then drawn through a nip formed between
tensioning rolls 322. The tensioning rolls 322 provide for proper takeoff
speed of the central lamina 30b from the chill roll 318 and further
provide for proper entry of the central lamina 30b into the combining
rolls 324. For pressure-sensitive foams, it may be desirable to use
tensioning rolls having release properties such as are known in the art in
order to prevent or minimize sticking of the foam to the rolls.
The outboard laminae 30a and 30c are taken from the unwind rolls 326a and
326c and preferably pass through S-wrap tensioning rolls 328a and 328c to
provide for proper tensioning to prevent puckering or bunching of the
outboard laminae 30a and 30c. If necessary, tracking systems 314a and
314c, as is commonly utilized and known in the art, may be employed to
optimally track and adjust the web of outboard laminae 30a and 30c into
the combining rolls 324. A tracking system manufactured by the Fife
Corporation of Oklahoma City, Okla., and sold as a Fife Guide Model No.
OP6 LRA is suitable.
The laminae 30a and 30c enter the combining rolls 324 generally parallel to
the travel of the laminate 30 as it passes through the nip of the
combining rolls 324. The nip of the combining rolls 324 compresses the
laminae 30a and 30c into contacting relationship with the opposed faces of
the central lamina 30b causing the central lamina 30b to bond to the
outboard laminae 30a and 30c --joining the three laminae 30a, 30b, and
30c.
If desired, the laminate 30 need not incorporate two outboard laminae 30a
and 30c. If desired, either or both outboard laminae 30a and 30c may be
omitted from the laminate 30. Such a structure may be manufactured by
selectively not operating the line 312a or 312c of the outboard lamina 30a
or 30c desired to be omitted. The resulting laminate 30 has one lamina 30b
or, for example, two laminae 30a and 30b with the lamina 30b being of
elastomeric adhesive foam and the lamina 30a being of relatively
inextensible substrate material. After a two laminae laminate 30 leaves
the nip of the combining rolls 324, the exposed face of the lamina 30b may
be deactivated, by an anti-blocking agent as is commonly known in the art,
so that the adhesive of the lamina 30b does not bond to other materials
through the pressure-sensitive properties of the adhesive making up the
foam of the lamina 30b. Anti-blocking is accomplished by the adhesive
deactivation system 330 applying a powder of resin to the exposed face of
the lamina 30b. Suitable resin powders include talcum powder, polyolefinic
powders, and preferably a resin similar to that used for the second lamina
30a. If desired, the adhesive deactivation system 330 may be applied to
the exposed face of the lamina 30b prior to the lamina 30a entering the
nip of the combining rolls 324. (It will be apparent to one skilled in the
an that an adhesive deactivation system 330 should not be employed prior
to the combining rolls 324 if a laminate 30 having two outboard laminate
30a and 30c is to be constructed using to the apparatus 310 of FIG. 1.)
The apparatus 310 can also have a secondary heating element, such as heated
rollers 332, to selectively provide localized heating to the zones of
laminate 30 in order to render the zones inelastic.
If desired, one or both of outboard laminae 30a and 30c may be elastically
extensible. The outboard laminae 30a and 30c may be or similar or
different materials, as desired. Alternatively, a film or nonuniform
thickness may be utilized for the outboard laminae 30a and 30c. As the
thickness of the film increases, a greater force will be required for the
same amount of extension to occur. The laminate 30 may be heat sealed as
desired.
The resultant laminate 30 can be described as a "zero strain" laminate,
i.e., the elastomeric adhesive foam is joined to the carrier in a
substantially untensioned condition (i.e., "zero strain").
In a preferred embodiment, at least a portion of the "zero strain" laminate
30 containing the elastomeric foam is then subjected to mechanical
stretching sufficient to permanently elongate the relatively inextensible
components of the laminate 30. The composite or elastomeric laminate is
then returned to its substantially untensioned condition so as to form a
"zero strain" stretch laminate. As used herein, the term "zero strain"
stretch laminate refers to a laminate comprised of at least two plies of
material which are secured to one another along at least a portion of
their coextensive surfaces while in a substantially untensioned ("zero
strain") condition; one of the plies comprising a material which is
stretchable and elastomeric (i.e., it will return substantially to its
untensioned dimensions after an applied tensile force has been released)
and a second ply which is elongate (but not necessarily elastomeric) so
that upon stretching the second ply will be, at least to a degree,
permanently elongated so that upon release of the applied tensile forces,
it will not fully return to its original undeformed configuration. "Zero
strain" stretch laminates are disclosed in U.S. Pat. No. 2,075,189 issued
to Galligan, et al. on Mar. 30, 1937: U.S. Pat. No. 3,025,199 issued to
Harwood on Mar. 13, 1962; U.S. Pat. No. 4,107,364 issued to Sisson on Aug.
15, 1978; U.S. Pat. No. 4,290,563 issued to Sisson on Jun. 24, 1980; and
U.S. Pat. No. 4.834,741 issued to Sabee on May 30, 1989. Each of these
patents are incorporated herein by reference.
Particularly preferred methods and apparatus used for making "zero strain"
stretch laminates out of a topsheet, a backsheet, and an elastomeric
member positioned between the same, use meshing corrugated rolls to
mechanically stretch the components. A discussion of suitable apparatus
and methods for mechanically stretching portions of a diaper is contained
in the hereinbefore referenced U.S. Pat. No. 4,107,364 issued to Sisson on
Aug. 15, 1978 and U.S. Pat. No. 4,834,741 issued to Sabee on May 30, 1989.
Particularly preferred apparatus and methods are disclosed in U.S. Pat.
No. 5,167,897 entitled "Improved Method and Apparatus for Incrementally
Stretching a Zero Strain Stretch Laminate Web to Impart Elasticity
Thereto"; issued to Gerald M. Weber, et al. on Dec. 1, 1992; U.S. Pat. No.
5,156,793 entitled "Improved Method and Apparatus for Incrementally
Stretching Zero Strain Stretch Laminate Web in a Non-Uniform Manner to
Impart a Varying Degree of Elasticity Thereto"; issued to Kenneth B.
Buell, et al. on Oct. 20, 1992; and U.S. Pat. No. 5,143,679 entitled
"Improved Method and Apparatus for Sequentially Stretching Zero Strain
Stretch Laminate Web to Impart Elasticity Thereto Without Rupturing the
Web"; issued to Gerald M. Weber, et al. on Sep. 1, 1992. The
specifications and drawings of each one of the foregoing applications are
incorporated herein by reference. Details of a particularly preferred
incremental stretching system which can be employed in making "zero
strain" stretch laminates are described in U.S. Pat. No. 5,151,092, issued
to Buell, et al., on Sept. 29, 1992, incorporated herein by reference.
In another embodiment, the lamina 30b may be operatively associated with
the laminae 30a and/or 30c in a tensioned condition (prestretched). After
prestretching the lamina 30b, the lamina 30b is joined with the second
lamina 30a and/or 30c. Upon release of the force causing prestretching of
the lamina 30b, the resulting laminate 30 gathers or contracts in the
direction of prestretching. Where a relatively inextensible outboard
lamina 30a and/or 30c is used, the resulting laminate 30 will be
elastically extensible to the extensibility limit of the laminae 30a or
30c. If the laminate 30 is elongated beyond the amount of prestretch of
the lamina 30b, the free length of the relatively inextensible outboard
lamina 30a and 30c will be exceeded. If this should occur, the
stress/strain experienced by the laminae 30a and 30c will sharply increase
without significant elongation and rupture of the laminae will likely
occur. Therefore, the lamina 30b should be prestretched to at least the
desired amount of elongation to obviate high stresses and strains on the
outboard laminae and rupture of the laminate. After rupture, the elastic
properties of the outboard laminae 30a and/or 30c would control further
elongation.
The central lamina 30b can be prestretched in one or more directions. If
the central lamina 30b is prestretched in two principal directions
(longitudinal and lateral, i.e., machine direction and cross-machine
direction, respectively), the resulting laminate 30 will contract in both
such directions, proportional to the magnitude of prestretching in each
principal direction. As used herein, the term "machine direction" refers
to the direction generally parallel to the travel of the laminate 30 as it
passes through the nip of the combining rolls 324, while "cross direction"
refers to the direction generally perpendicular to the travel of the
laminate 30 as it passes through the nip of the combining rolls 324.
The central lamina 30b may be prestretched by any means known in the art.
For example, the surface speed of the combining rolls 324 may be greater
than the surface speed of the tensioning rolls 322. This causes
prestretching of the central lamina 30b in the machine direction, which
prestretching is proportional to the differential surface velocity between
the combining rolls 324 and the tensioning rolls 322, and the distance
therebetween. Prestretching in the cross direction can occur by methods
such as are known in the art, e.g., by tentering the lamina using, e.g., a
Mt. Hope roll, grooved roll, or an expanding conveyor and a cam.
In yet another embodiment, the elastomeric adhesive foam may alternatively
be operatively associated with the outboard lamina 30a and 30c in a
tensioned condition (prestretched), followed by mechanical stretching of
the laminate 30 to form a mechanically stretched, pretensioned, stretch
laminate.
In still another embodiment of the present invention, at least a portion of
the relatively inextensible laminae 30a and/or 30c is subjected to
mechanical stretching prior to lamination with the central lamina 30b in
order to provide both a "zero strain" stretch laminate and to prestrain
the portion of the inextensible lamina. The outboard laminae may be
prestretched in the same manner described in reference to the central
lamina 30b.
The lamina 30b may be in the form or a continuous sheet. In a preferred
embodiment, the lamina 30b is formed as a continuous sheet on a backsheet
material as described herein. Lamina 30a then preferably comprises a
topsheet material as described herein. Alternatively, the lamina 30b may
be shaped as previously described, for example, by molding such as in a
rotary mold. The shaped lamina 30b is then affixed to a backsheet material
(lamina 30b) so as to elasticize particular portions of a disposable
absorbent article after joinder with other components of the article.
In an alternative embodiment, the elastomeric adhesive foam is formed by an
intermediate process as described herein for subsequent association with a
permanent carrier. The foam can be formed on release paper, e.g., using
apparatus as shown and described for apparatus 310, wherein at least one
of the material unwind rolls is release paper. (The foam may also be
formed on a transfer web such as known in the art). The foam may then be
wound upon itself for later joinder to a carrier. The foam can be joined
to the permanent carrier in a non-tensioned condition to form a "zero
strain" laminate as previously described. Alternatively, the elastomeric
adhesive foam may be associated with the carrier in an elastically
contractible (prestretched) condition so that the elastomeric adhesive
foam gathers or contracts the carrier upon release of the force used to
prestretch the foam. A more detailed description of the manner in which an
elastomeric material may be secured in an absorbent article in an
elastically contractible condition can be found in U.S. Pat. No.
3,860,033, issued to Buell on Jan. 14, 1975, and in U.S. Pat. No.
4,081,301, issued to Buell on Mar. 28, 1978; both patents being
incorporated herein by reference. For example, the elastomeric adhesive
foam can be contractibly affixed to the carrier by laterally extending,
the elastomeric adhesive foam member, affixing the elastomeric adhesive
foam to the carrier, and allowing the adhesive foam to assume its relaxed
or uncontracted orientation. (The previously described shaped lamina 30b
may also be contractibly affixed to a carrier in such manner in a
continuous process). The resultant "zero strain" laminate or pre-stretched
laminate may be mechanically stretched as previously described to form a
"zero strain" stretch laminate or a pre-tensioned stretch laminate,
respectively.
The elastomeric adhesive foams and laminates are particularly useful to
impart compressibility, resilience, and/or elasticity to absorbent
articles. Entire panels of such articles or portions thereof may thus be
made compressible, resilient, and/or elastic. As used herein, the term
"absorbent article" refers to devices which absorb and contain body
exudates, and, more specifically, refers to devices which are placed
against or in proximity to the body of the wearer to absorb and contain
the various exudates discharged from the body. The term "disposable" is
used herein to describe absorbent articles which are not intended to be
laundered or otherwise restored or reused as an absorbent article (i.e.,
they are intended to be discarded after a single use and, preferably, to
be recycled, composted or otherwise disposed of in an environmentally
compatible manner). A "unitary" absorbent article refers to absorbent
articles which are formed of separate parts united together to form a
coordinated entity so that they do not require separate manipulative parts
like a separate holder and liner. A preferred embodiment of an absorbent
article of the present invention is the unitary disposable absorbent
article, diaper 20, shown in FIG. 3. As used herein, the term "diaper"
refers to an absorbent article generally worn by infants and incontinent
persons that is worn about the lower torso of the wearer. It should be
understood, however, that the present invention is also applicable to
other absorbent articles such as incontinent briefs, incontinent
undergarments, diaper holders and liners, training pants, feminine hygiene
garments, and the like.
FIG. 3 is a plan view of the diaper 20 of the present invention in its
flat-out, uncontracted state (i.e., with elastic induced contraction
pulled out except in the side panels wherein the elastic is left in its
relaxed condition) with portions of the structure being cut-away to more
clearly show the construction of the diaper 20 and with the portion of the
diaper 20 which faces away from the wearer, the outer surface 52, facing
the viewer. As shown in FIG. 3, the diaper 20 comprises a containment
assembly 22 preferably comprising a liquid pervious topsheet 24, a liquid
impervious backsheet 26 joined with the topsheet 24, and an absorbent core
28 positioned between the topsheet 24 and the backsheet 26, elasticized
side panels 30; elasticized leg cuffs 32; an elastic waist feature 34; and
a closure system comprising a dual tension fastening system generally
multiply designated as 36.
The diaper 20 is shown in FIG. 3 to have an outer surface 52 (facing the
viewer in FIG. 3), an inner surface 54 opposed to the outer surface 52, a
first waist region 56, a second waist region 58 opposed to the first waist
region 56, and a periphery 60 which is defined by the outer edges of the
diaper 20 in which the longitudinal edges are designated 62 and the end
edges are designated 64. (While the skilled artisan will recognize that a
diaper is usually described in terms of having a pair of waist regions and
a crotch region between the waist regions; in this application, for
simplicity of terminology, the diaper 20 is described as having only waist
regions, each of the waist regions including a portion of the diaper which
would typically be designated as part of the crotch region). The inner
surface 54 of the diaper 20 comprises that portion of the diaper 20 which
is positioned adjacent to the wearer's body during use (i.e., the inner
surface 54 generally is formed by at least a portion of the topsheet 24
and other components joined to the topsheet 24). The outer surface 52
comprises that portion of the diaper 20 which is positioned away from the
wearer's body (i.e., the outer surface 52 generally is formed by at least
a portion of the backsheet 26 and other components joined to the backsheet
26). (As used herein, "body surface" refers to the surface facing the
wearer's body; "garment surface" refers to the surface facing away from
the wearer's body). The first waist region 56 and the second waist region
58 extend, respectively, from the end edges 64 of the periphery 60 to the
lateral centerline 66 of the diaper 20. The waist regions each comprise a
central region 68 and a pair of side panels which typically comprise the
outer lateral portions of the waist regions. The side panels positioned in
the first waist region 56 are designated 70 while the side panels in the
second waist region 58 are designated 72. (In the discussion that follows,
unless otherwise noted, the diaper 20 will comprise a pair of side panels
in each waist region. While it is not necessary that the pairs of side
panels or each side panel be identical, they are preferably mirror images
one of the other.) In a preferred embodiment of the present invention, the
side panels 72 positioned in the second waist region 58 are elastically
extensible in the lateral direction (i.e., elasticized side panels 30).
(The lateral direction (.times.direction or width) is defined as the
direction parallel to the lateral centerline 66 of the diaper 20; the
longitudinal direction (y direction or length) being defined as the
direction parallel to the longitudinal centerline 67, and the axial
direction (Z direction or thickness) being defined as the direction
extending through the thickness of the diaper 20.)
FIG. 3 shows a preferred embodiment of the diaper 20 in which the topsheet
24 and the backsheet 26 have length and width dimensions generally larger
than those of the absorbent core 28. The topsheet 24 and the backsheet 26
extend beyond the edges of the absorbent core 28 to thereby form the
periphery 60 of the diaper 20. While the topsheet 24, the backsheet 26,
and the absorbent core 28 may be assembled in a variety of well known
configurations, preferred diaper configurations are described generally in
U.S. Pat. No. 3,860,003 entitled "Contractible Side Portions for
Disposable Diaper" which issued to Kenneth B. Buell on Jan. 14, 1975: and
U.S. Pat. No. 5,151,092 entitled "Absorbent Article With Dynamic Elastic
Waist Feature Having A Predisposed Resilient Flexural Hinge" which issued
to Kenneth B. Buell et al. on Sep. 29, 1992; each of which is incorporated
herein by reference. Alternatively preferred configurations for disposable
diapers herein are also disclosed in U.S. Pat. No. 4,808,178 issued to
Aziz et al. on Feb. 28, 1989; U.S. Pat. No. 4,695,278 issued to Lawson on
Sep. 27, 1987; and U.S. Pat. No. 4,816,025 issued to Foreman on Mar. 28,
1989. These patents are incorporated herein by reference.
FIG. 4 is a cross-sectional view of the diaper 20 taken along section line
4--4 of FIG. 3 in the first waist region 56. FIG. 4 shows a construction
of the elasticized waistband 35 of the elastic waist feature 34. The
elasticized waistband 35 is shown in FIG. 4 in its contracted or relaxed
condition. The elasticized waistband 35 preferably comprises a portion of
the topsheet 24, a portion of the backsheet 26 that has preferably been
mechanically stretched, and an elastomeric member 76 positioned between
the topsheet 24 and the backsheet 26. The elastomeric member 76 preferably
comprises the elastomeric adhesive foam of the present invention. Although
not necessary for practicing the present invention, the elasticized
waistband can also comprise a resilient member 77, preferably positioned
between the backsheet 26 and the elastomeric member 76 as shown in FIG. 4.
The resilient member is suitably as described in U.S. Pat. No. 5, 151,092
issued to Buell et al. on Sep. 29, 1992, incorporated herein by reference.
Thus, although the adhesive foam of the present invention is itself
resilient, the elasticized waistband can contain additional resilient
members such as described in U.S. Pat. No. 5,151,092.
FIG. 5 is a fragmentary cross-sectional view of the diaper 20 taken along
line 5--5 of FIG. 3 and depicts an elastic waist feature construction in
the first waist region 56. The absorbent core 28 is generally shown in
FIG. 5 and shows the waist edge 83 and the garment surface 100 of the
absorbent core 28. The topsheet 24 and the backsheet 26 encase the
absorbent core 28 and extend longitudinally outwardly beyond the waist
edge 83 of the absorbent core 28 to form a waist flap 89 (also shown in
FIG. 3) and the end edge 64. The elastic waist feature 34 extends
longitudinally outwardly from the waist edge 83 of the absorbent core 28
in at least the central region 68 and forms at least a portion of the end
edge 64. The elastic waist feature 34 comprises an interconnecting panel
zone 130, a first flexural hinge zone 132 joining the interconnecting
panel zone 130 with the containment assembly 22 adjacent the waist edge 83
of the absorbent core 28, an elasticized waistband 35, and a second
flexural hinge zone 134 joining the elasticized waistband 35 with the
interconnecting panel zone 130. As shown in FIG. 5, the elasticized
waistband 35 comprises a shaping panel zone 136, a waistline panel zone
138, and a predisposed, resilient, waistband flexural hinge zone 140
joining the shaping panel zone 136 and the waistline panel zone 138. The
interconnecting panel zone 130 comprises a portion of the topsheet 24 and
the backsheet 26 while the elasticized waistband 35 comprises a portion of
the topsheet 24 and the backsheet 26 and the elastomeric member 76. As
shown in FIG. 5, the elasticized waistband can comprise a resilient member
77 as previously described herein.
The containment assembly 22 of the diaper 20 is shown in FIG. 3 as
comprising the main body (chassis) of the diaper 20. The containment
assembly 22 comprises at least an absorbent core 28 and preferably an
outer covering layer comprising the topsheet 24 and the backsheet 26. When
the absorbent article comprises a separate holder and a liner, the
containment assembly 22 generally comprises the holder and the liner (i e,
the containment assembly 22 comprises one or more layers of material to
define tile holder while the liner comprises an absorbent composite such
as a topsheet, a backsheet, and an absorbent core) For unitary absorbent
articles, the containment assembly 22 comprises the main structure of the
diaper with other features added to form the composite diaper structure.
Thus, the containment assembly 22 for the diaper 20 generally comprises
the topsheet 24, the backsheet 26, and the absorbent core 28.
The absorbent core 28 may be any absorbent means which is generally
compressible, conformable, non-irritating to the wearer's skin, and
capable of absorbing and retaining liquids such as urine and other certain
body exudates. As shown in FIG. 3, the absorbent core 28 has a garment
surface 100, a body surface 102, side edges 82, and waist edges 83. The
absorbent core 28 may be manufactured in a wide variety of sizes and
shapes (e g., rectangular, hourglass. "T"-shaped, asymmetric, etc.) and
from a wide variety of liquid-absorbent materials commonly used in
disposable diapers and other absorbent articles such as comminuted wood
pulp which is generally referred to as airfelt. Examples of other suitable
absorbent materials include creped cellulose wadding; meltblown polymers
including conform, chemically stiffened, modified or cross-linked
cellulosic fibers; tissue including tissue wraps and tissue laminates;
absorbent foams; absorbent sponges; superabsorbent polymers, absorbent
gelling materials; or any equivalent material or combinations of
materials. The configuration and construction of the absorbent core may
also be varied (e g. the absorbent core may have varying caliper zones, a
hydrophilic gradient, a superabsorbent gradient, or lower average density
and lower average basis weight acquisition zones; or may comprise one or
more layers or structures). The total absorbent capacity of the absorbent
core 28 should, however, be compatible with the design loading and the
intended use of the diaper 20. Further, the size and absorbent capacity of
the absorbent core 28 may be varied to accommodate wearers ranging from
infants through adults. Exemplary absorbent structures for use as the
absorbent core 28 are described in U.S. Pat. No. 4,610,678 entitled
"High-Density Absorbent Structures" issued to Weisman et al. on Sep. 9,
1986; U.S. Pat. No. 4,673,402 entitled "Absorbent Articles With
Dual-Layered Cores" issued to Weisman et al. on Jun. 16, 1987; U.S. Pat.
No. 4,888,231 entitled "Absorbent Core Having A Dusting Layer" issued to
Angstadt on Dec. 19, 1989; and U.S. Pat. No. 4,834,735, entitled "High
Density Absorbent Members Having Lower Density and Lower Basis Weight
Acquisition Zones", issued to Alemany el al. on May 30, 1989. Each of
these patents are incorporated herein by reference.
The absorbent core 28 may contain the elastomeric adhesive foam of the
present invention. For example, the foam may be incorporated in laminate
form, the laminate comprising at least one lamina consisting of any of the
forementioned liquid-absorbent materials joined to at least one lamina of
the elastomeric adhesive foam of the present invention. Such laminates may
be made by any of the methods as described herein. Typically a "zero
strain" laminate will be used in the absorbent core area.
The backsheet 26 is positioned adjacent the garment surface 100 of the
absorbent core 28. In a preferred embodiment, the backsheet 26 is joined
to the absorbent core by the elastomeric adhesive foam. (As used herein,
the term "joined" encompasses configurations whereby an element is
directly secured to the other element by affixing the element directly to
the other element, and configurations whereby the element is indirectly
secured to the other element by affixing the element to intermediate
member(s) which in turn are affixed to the other element.) For example, a
trilaminate may be formed as previously described in which one material
unwind roll supplies a backsheet material and the other material unwind
roll supplies a topsheet material. The absorbent core material is provided
by means such as are known in the art, e.g., by using a vacuum forming
pocket roll and a transfer web, and is affixed to the foam lamina so as to
leave some portion of the foam lamina exposed, preferably the portion
around the periphery of the core. The topsheet material is then affixed to
the exposed foam lamina to effect joinder with the backsheet. The
absorbent core material may alternatively be joined to the topsheet 24
prior to lamination with the backsheet 26.
In a preferred embodiment the elastomeric adhesive foam covers
substantially all of the backsheet lamina. The resultant bilaminate can
then be combined with the absorbent core 28 in a manner such that a
portion of the adhesive foam remains exposed, preferably a portion around
the entire periphery of the absorbent core. The topsheet 24 may then be
affixed to the backsheet via the adhesive properties of the foam so as to
form the diaper 20.
In an alternative embodiment, the adhesive foam is patterned on the
backsheet lamina by means described herein. Preferably the foam is
patterned onto those areas of the backsheet in which it is desirable to
impart resilience, compressibility, elasticity, and/or adhesive properties
without the use of external bonding agents. For example, the foam can be
patterned onto the backsheet in those areas corresponding to the
elasticized side panels 30, elastic waist feature 34, and/or elasticized
leg cuffs 32. The foam may also be patterned onto areas to effect joinder
of the absorbent core 28 and/or topsheet 24 via the adhesive properties of
the foam. The foam pattern corresponding to the area between the absorbent
core and the backsheet need not cover the entire area. For example, the
pattern can be such to impart compressibility to areas particularly
subjected to pressure while the diaper 20 is in use.
The backsheet 26, absorbent core material 28, and the elastomeric adhesive
foam can be laminated by any of the methods previously described,
including a pre-tensioned laminate, a "zero strain" laminate, a "zero
strain" stretch laminate, and a mechanically stretched, pre-tensioned
stretch laminate. In a preferred embodiment, a "zero strain" laminate of
the backsheet 26, the absorbent core 28, and the topsheet 24 is formed.
Portions of the resultant "zero strain" laminate are then mechanically
stretched to form a "zero strain" stretch laminate. Mechanical stretching
is preferably performed on those regions corresponding to the elasticized
side panels 30, the elastic waist feature 34, and/or the elasticized leg
cuffs 32.
In an alternative embodiment, the backsheet and absorbent core are joined
by attachment means (not shown) such as those well known in the art. For
example, the backsheet 26 may be secured to the absorbent core 28 by a
uniform continuous layer of adhesive, a patterned layer of adhesive, or an
array of separate lines, spirals, or spots of adhesive. Adhesives which
have been found to be satisfactory are manufactured by H. B. Fuller
Company of St. Paul, Minn. and marketed as HL-1258. The attachment means
will preferably comprise an open pattern network of filaments of adhesive
as is disclosed in U.S. Pat. No. 4,573,986, entitled "Disposable
Waste-Containment Garment", which issued to Minetola, et al. on Mar. 4,
1986, more preferably several lines of adhesive filaments swirled into a
spiral pattern such as is illustrated by the apparatus and methods shown
in U.S. Pat. No. 3,911,173, issued to Sprague, Jr. on Oct. 7, 1975; U.S.
Pat. No. 4,785,996, issued to Ziecker, et al. on Nov. 22, 1978; and U.S.
Pat. No. 4,842,666, issued to Werenicz on Jun. 27, 1989. Each of these
patents are incorporated herein by reference. Alternatively, the
attachment means may comprise heat bonds, pressure bonds, ultrasonic
bonds, dynamic mechanical bonds, or any other suitable attachment means or
combinations of these attachment means as are known in the art.
The backsheet 26 is impervious to liquids (e.g., urine) and is preferably
manufactured from thin plastic film, although other flexible liquid
impervious materials may also be used. As used herein, the term "flexible"
refers to materials which are compliant and will readily conform to the
general shape and contours of the human body. The backsheet 26 prevents
the exudates absorbed and contained in the absorbent core 28 from wetting
articles which contact the diaper 20 such as bedsheets and undergarments.
The backsheet 26 may thus comprise a woven or nonwoven material, polymeric
films such as thermoplastic films of polyethylene or polypropylene, or
composite materials such as a film-coated nonwoven material. Preferably,
the backsheet comprises a thermoplastic film having a thickness of from
about 0.012 mm (0.5 mil to about 0.051 mm (2.0 mils). Particularly
preferred materials for the backsheet include RR8220 blown films and
RR5475 cast films as manufactured by Tredegar Industries, Inc. of Terre
Haute, Ind. The backsheet 26 is preferably embossed and/or matte finished
to provide a more clothlike appearance. Further, the backsheet 26 may
permit vapors to escape from the absorbent core 28 (i.e., breathable)
while still preventing exudates from passing through the backsheet 26.
In a preferred embodiment of the present invention, at least a portion of
the backsheet 26 is subjected to mechanical stretching as described herein
in order to provide both a "zero strain" stretch laminate that forms the
elasticized side panels 30 and to prestrain the portion of the backsheet
coinciding with the elastic waist feature 34. Thus, the backsheet 26 is
preferably elongatable, most preferably drawable, but not necessarily
elastomeric, so that the backsheet 26 will, upon mechanical stretching, be
at least to a degree permanently elongated such that it will not fully
return to its original undistorted configuration. In preferred
embodiments, the backsheet can be subjected to mechanical stretching
without undue rupturing or tearing. Thus, it is preferred that the
backsheet 26 have an ultimate elongation to break of at least about 400%
to about 700% in the cross-machine direction as measured using a method
consistent with ASTM D-638. The above noted ER8220 and RR5475 blends are
suitable backsheet materials.
In yet another embodiment, the backsheet may be a laminate comprising at
least one lamina of any of the foregoing backsheet materials and at least
one lamina of the elastomeric adhesive foam of the present invention. For
example, the backsheet laminate can comprise the elastomeric adhesive foam
as a central lamina between two lamina of any of the foregoing backsheet
materials, e.g., a nonwoven. The laminate may be formed by any of the
methods described herein. Typically, a "zero strain" laminate will be
formed. Preferably, at least a portion of the "zero strain" laminate is
subjected to mechanical stretching in order to provide both a "zero
strain" stretch laminate that forms the elasticized side panels 30 and to
prestrain the portion of the backsheet 26 laminate coinciding with the
elastic waist feature, as previously described. In yet another embodiment,
the backsheet lamina(e) of the laminate is prestretched as described
herein. The laminate can then be constructed and incorporated into the
diaper 20 as previously described.
The topsheet 24 is positioned adjacent the body surface of the absorbent
core 28 and is preferably joined thereto and to the backsheet 26 by the
elastomeric adhesive foam in the manner described in reference to joinder
of the backsheet 26 and absorbent core 25. Alternatively, the topsheet can
be joined to those components by attachment means (not shown) such as
those well known in the art. Suitable attachment means are described with
respect to joining the backsheet 26 to the absorbent core 28. In a
preferred embodiment of the present invention, the topsheet 24 and the
backsheet 26 are joined directly to each other in the diaper periphery 60
by the adhesive foam and are indirectly joined together by directly
joining them to the absorbent core 28 by the elastomeric adhesive foam
and/or other attachment means (not shown).
The topsheet 24 is compliant, soft feeling, and non-irritating to the
wearer's skin. Further, the topsheet 24 is liquid pervious permitting
liquids (e.g., urine) to readily penetrate through its thickness. A
suitable topsheet may be manufactured from a wide range of materials, such
as porous foams; reticulated foams; apertured plastic films; or woven or
nonwoven webs of natural fibers (e.g., wood or cotton fibers), synthetic
fibers (e.g., polyester or polypropylene fibers), or a combination of
natural and synthetic fibers. There are a number of manufacturing
techniques which may be used to manufacture the topsheet 24. For example,
the topsheet 24 may be a nonwoven web of fibers spunbonded, carded,
wet-laid, meltblown, hydroentangled, combinations of the above, or the
like. A preferred topsheet is carded and thermally bonded by means well
known to those skilled in the fabrics art. A preferred topsheet comprises
a web of staple length polypropylene fibers such as is manufactured by
Veratec, Inc., a Division of International Paper Company, of Walpole,
Mass. under the designation P-8.
In a preferred embodiment of the present invention, at least a portion of
the topsheet 24 is subjected to mechanical stretching as described herein
in order to provide a "zero strain" stretch laminate that forms the
elasticized side panels 30. Thus, the topsheet 24 is preferably
elongatable, most preferably drawable, but not necessarily elastomeric, so
that the topsheet 24 will, upon mechanical stretching, be at least to a
degree permanently elongated such that it will not fully return to its
original configuration. In preferred embodiments, the topsheet 24 can be
subjected to mechanical stretching without undue rupturing or tearing of
the topsheet. Thus, it is preferred that the topsheet 24 have a low
cross-machine direction (lateral direction) yield strength. The P-8
topsheet (Veratec, Inc) is a suitable topsheet material.
In yet another embodiment, the topsheet 24 may be a laminate comprising at
least one lamina of any of the foregoing topsheet materials and at least
one lamina of the elastomeric adhesive foam of the present invention. The
topsheet 24 laminate may be formed in the manner described for the
backsheet 26 laminate. Preferably, at least a portion of the topsheet 24
laminate is subjected to mechanical stretching in order to form a
zero-strain stretch laminate that forms the elasticized side panels 30. In
a preferred embodiment, the topsheet 24 laminate has a configuration as
described in U.S. Pat. No. 5,037,416 issued to Allen, et al. on Aug. 6,
1991. The topsheet laminate preferably has a liquid pervious zone as
described therein.
The diaper 20 preferably further comprises elasticized leg cuffs 32 for
providing improved containment of liquids and other body exudates. Each
elasticized leg cuff 32 may comprise several different embodiments for
reducing the leakage of body exudates in the leg regions. (The leg cuff
can be and is sometimes also referred to as leg bands, side flaps, barrier
cuffs, or elastic cuffs.) U.S. Pat. No. 3,860,003, issued to Buell on Jan.
14, 1975 (Reexamination Certificate BI 3,860,003 issued Apr. 18, 1989),
describes a disposable diaper which provides a contractible leg opening
having a side flap and one or more elastic members to provide an
elasticized leg cuff (gasketing cuff). U.S. Pat. No. 4,909,803, entitled
"Disposable Absorbent Article Having Elasticized Flaps" issued to Aziz et
al. on Mar. 20, 1990, describes a disposable diaper having "stand-up"
elasticized flaps (barrier cuffs) to improve the containment of the leg
regions. U.S. Pat. No. 4,695,278, entitled "Absorbent Article Having Dual
Cuffs" issued to Lawson on Sep. 22, 1987, describes a disposable diaper
having dual cuffs including a gasketing cuff and a barrier cuff. While
each elasticized leg cuff 32 may be configured so as to be similar to any
of the leg bands, side flaps, barrier cuffs, or elastic cuffs described
above, it is preferred that each elasticized leg cuff 32 comprise at least
an inner barrier cuff comprising a barrier flap and a spacing elastic
member such as described in the above referenced U.S. Pat. No. 4,909,803.
In a preferred embodiment, the elasticized leg cuff additionally comprises
an elastic gasketing cuff with one or more elastic strands positioned
outboard of the barrier cuff such as described in the above referenced
U.S. Pat. No. 4,695,278.
The elastic members of the leg cuffs may comprise the elastomeric adhesive
foam of the present invention. In a preferred embodiment, the elastic
members are formed by mechanically stretching those regions of a "zero
strain" laminate previously formed in at least the cuff regions.
Alternatively, the elastomeric adhesive foam may be incorporated into the
cuff by forming the foam in a rotary mold having a shape suitable for the
elastic member. The shaped elastomeric adhesive foam may then be
pre-stretched and affixed in a contractible condition. The shaped foam may
alternatively be laminated in an untensioned condition in the leg cuff,
followed by mechanically stretching the laminated portions so as to form a
"zero strain" stretch laminate in the cuff region. In yet another
embodiment, the foam is applied prestretched followed by mechanical
stretching to form a mechanically stretched, pretensioned, stretch
laminate.
The diaper 20 preferably further comprises an elastic waist feature 34 that
provides improved fit and containment. The elastic waist feature 34 is
that portion or zone of the diaper 20 which is intended to elastically
expand and contract to dynamically fit the wearer's waist. The elastic
waist feature 34 at least extends longitudinally outwardly from at least
one of the waist edges of the absorbent core 28 and generally Forms at
least a portion of the end edge 64 of the diaper 20. Disposable diapers
are generally constructed so as to have two elastic waist features, one
positioned in the first waist region and one positioned in the second
waist region, although diapers can be constructed with a single elastic
waist feature. Further, while the elastic waist feature or any of its
constituent elements can comprise a separate element affixed to the diaper
20, the elastic waist feature 34 is preferably constructed as an extension
of other elements of the diaper such as the backsheet 26 or the topsheet
24, preferably both the backsheet 26 and the topsheet 24.
The elasticized waistband 35 of the elastic waist feature 34 may be
constructed in a number of different configurations including those
described in U.S. Pat. No. 4,515,595, issued to Kievit et al. on May 7,
1985, incorporated herein by reference; and the above referenced U.S. Pat.
No. 5,151,092, issued to Buell, et al. on Sep. 29, 1992. The elasticized
waistband of the elastic waist feature preferably comprises the
elastomeric adhesive foam of the present invention.
In a particularly preferred embodiment, the elastic waist feature is
constructed according to any of the waist feature configurations described
in the above referenced U.S. Pat. No. 5,151,092, issued to Buell, et al.
on Sep. 29, 1992, in which the elastomeric member 76 of the elasticized
waistband 35 comprises the elastomeric adhesive foam of the present
invention. As shown in FIG. 4, the elasticized waistband 35 preferably
comprises at least three materials laminated together. The elasticized
waistband 35 preferably comprises a portion of the topsheet 24; a portion
of the backsheet 26, this portion of the backsheet being preferably
"mechanically prestrained"; and an elastomeric member 76 comprising the
elastomeric adhesive foam of the present invention. The elasticized
waistband can also comprise a resilient member 77. The resilient member 77
is preferably joined to the elastomeric member 76 with the resilient
member 77 disposed toward the backsheet 26 and the elastomeric member 76
disposed toward the topsheet 24. The elastomeric member 76 and the
resilient member are also shown in FIG. 3.
While the preferred elastic waist feature 34 need only comprise an
elasticized waistband and a flexural hinge zone joining the elasticized
waistband with the containment assembly 22; as shown in FIG. 5 the elastic
waist feature 34 more preferably comprises several additional zones such
as described in the above referenced U.S. Pat. No. 5,151,092 issued to
Buell, et at., incorporated herein by reference. In particular, the
elastic waist feature 34 comprises an interconnecting panel zone 130, a
first flexural hinge zone 132 joining the interconnecting panel zone 130
with the containment assembly 22 adjacent the waist edge 83 of the
absorbent core 28, an elasticized waistband 35, and a second flexural
hinge zone 134 joining the elasticized waistband 35 with the
interconnecting panel zone 130. The interconnecting panel zone 130
preferably provides a flexible link between the elasticized waistband 35
and the containment assembly 22. The elasticized waistband 35 provides a
member that maintains a defined area coverage, contacts the wearer's
waist, and is elastically extensible in at least the lateral direction so
as to dynamically fit against the waist of the wearer and to dynamically
conform to the waist of the wearer so as to provide improved fit. As shown
in FIG. 5, the elasticized waistband 35 comprises a shaping panel zone
136; a waistline panel zone 138; and a predisposed, resilient, waistband
flexural hinge zone 140 joining the shaping panel zone 136 and the
waistline panel zone 138. As used herein, the term "zone" is used to
denote an area or element of the elastic waist feature 34. While a zone of
the elastic waist feature 34 may be a distinct area or element; typically,
a zone of the elastic waist feature will overlap somewhat with an adjacent
zone(s). (For illustration purposes, the zones are delineated with
brackets in FIG. 5.)
The elastomeric member 76 is operatively associated with the elasticized
waistband 35, preferably between the topsheet 24 and the backsheet 26. so
that the elastomeric member 76 allows the elasticized waistband 35 to be
elastically extensible in the lateral direction (i.e.. laterally
elastically extensible), and so that it can contractively return to its
substantially unrestrained configuration.
The elastomeric member 76 can be operatively associated in the elasticized
waistband 35 in a number of different ways. In a preferred embodiment, the
elastomeric member 76 is associated in the elasticized waistband 35 in the
form of a "zero strain" laminate. In a preferred embodiment, at least the
regions of the "zero strain" laminate corresponding to the elasticized
waist band 35 are mechanically stretched to form a "zero strain" stretch
laminate.
In an alternative embodiment, the elastomeric member may be operatively
associated in an elastically contractible condition as described herein so
that the elastomeric member gathers or contracts the elasticized
waistband. For example, the elastomeric member may be a shaped foam (e.g.,
as prepared in a rotary mold). The shaped elastomeric members 76 can be
contractibly affixed in the elasticized waistband 35 by laterally
extending the elastomeric member 76, affixing the elastomeric member 76 to
either or both the topsheet 24 and the backsheet 26, and allowing the
elastomeric member 76 to assume its relaxed or contracted orientation.
Alternatively, the shaped elastomeric member 76 can be operatively
associated in the elasticized waistband 35 by securing the elastomeric
member 76 to the topsheet 24, the backsheet 26, or both while the
elastomeric member 76 is in a substantially untensioned condition (i.e.,
"zero strain"), at least a portion of the laminate containing the
elastomeric member 76 then being subjected to mechanical stretching
sufficient to permanently elongate the topsheet 24 and the backsheet 26
components of the laminate, followed by returning the composite or
elastomeric laminate to its substantially untensioned condition to form a
"zero strain" stretch laminate. Any of the methods previously described
for forming a "zero strain" stretch laminate may be used. The elastomeric
member 76 may alternatively be operatively associated in a tensioned
condition (prestretched or pretensioned) followed by mechanical stretching
to form a mechanically stretched, pretensioned, stretch laminate, as
described herein.
The elastomeric members 76 useful in the present invention may take on a
number of different sizes, shapes, configurations, and materials. For
example, the elasticized waistband 35 may be formed from one or a
plurality or elastomeric members operatively associated between the
topsheet and the backsheet; the elastomeric member 76 may have varying
widths and lengths; or the elastomeric member 76 may comprise relatively
narrow strands of elastomeric material or a larger area patch of
elastomeric material. In addition to the elastomeric adhesive foams of the
present invention, the elastomeric member may also include known
materials, e.g. elastomeric foam such as the polyurethane foam available
from Bridgestone of Yokahama, Japan and designated Bridgestone SG
Polyurethane Foam. Other suitable elastomeric materials for use in the
elastomeric member 76 include "live" synthetic or natural rubber,
elastomeric films (including heat-shrinkable elastomeric films), formed
elastomeric scrim, or the like. Where such conventional elastomers are
used, it may be necessary or desired to use external bonding agents as are
known in the art to operatively associate the elastomeric member 76 with
another diaper component.
In a preferred embodiment of the present invention, the portion of the
backsheet 26 forming the elasticized waistband 35 has been "prestrained"
or "mechanically prestrained" (i.e., subjected to some degree of localized
pattern mechanical stretching to permanently elongate those portions of
the backsheet forming the elasticized waistband 35). A prestrained
backsheet improves the extension and contraction of the elastomeric member
76. The backsheet 26 of the present invention can be prestrained as
described in the above referenced U.S. Pat. No. 5,151,092 issued to Buell,
et al. on Sep. 29, 1992, e.g., by directing the backsheet through an
incremental mechanical stretching system as described therein. The
backsheet can alternatively be prestrained by using deep embossing
techniques as are known in the art.
In a preferred method for making the diapers of the present invention,
after the backsheet web has been prestrained, and after the backsheet web
has been removed from the corrugated combining rolls, a laminate
comprising a center lamina of the elastomeric adhesive foam of the present
invention positioned between a lamina of the prestrained backsheet and a
lamina of the topsheet is formed as previously described to form the
elasticized waistband 35.
In an alternative embodiment, the elasticized waistband in the second waist
region 58 (or the first waist region 56 if elasticized side panels are
disposed therein) and the elasticized side panels 30 can comprise a
continuous elastomeric member, e.g., a continuous piece of the elastomeric
adhesive foam, in both the side panels 72 and the central region 68 of the
second waist region 58. Thus, the elasticized waistband 35 and the
elasticized side panels 30 can be formed from the same piece of
elastomeric adhesive foam to form a unitary structure. An example of such
an elasticized waistband/side panel configuration is disclosed in the
hereinbefore referenced U.S. Pat. No. 4,887,067, issued to Wood, et al. on
Aug. 15, 1989, and which patent is incorporated herein by reference.
In a further alternative embodiment of the present invention, the
elasticized waistband 35 may have differential extensibility along the
longitudinal axis when stretched in the lateral direction. The
differential extensibility of the elasticized waistband 35 allows portions
to laterally expand to a greater degree than other portions along the
longitudinal axis. This differential extensibility of the elasticized
waistband provides an abdominally compliant elasticized waistband, i.e.,
an "expansive tummy panel", that allows the elasticized waistband to
differentially shape, expand, and move with the stomach of the wearer as
the wearer moves, sits, and stands. Differential extensibility along the
longitudinal axis when stretched in the lateral direction of the
elasticized waistband can be achieved in a number of ways such as is
discussed with respect to the elasticized side panels 30. A preferred
differential extensibility elasticized waistband has a pentagonal shape.
In a preferred embodiment, the diaper also comprises elasticized side
panels 30 disposed in the second waist region 58. (As used herein, the
term "disposed" is used to mean that an element(s) of the diaper is formed
(joined and positioned) in a particular place or position as a unitary
structure with other elements of the diaper or as a separate element
joined to another element of the diaper.) The elasticized side panels 30
provide an elastically extensible feature that provides a more comfortable
and contouring fit by initially conformably fitting the diaper to the
wearer and sustaining this fit throughout the time of wear well past when
the diaper has been loaded with exudates since the elasticized side panels
allow the sides of the diaper to expand and contract. The elasticized side
panels 30 further provide more effective application of the diaper 20
since even if the diaperer pulls one elasticized side panel 30 farther
than the other during application (asymmetrically), the diaper 20 will
"self-adjust" during wear. While the diaper 20 of the present invention
preferably has the elasticized side panels 30 disposed in the second waist
region 58; alternatively, the diaper 20 may be provided with elasticized
side panels 30 disposed in the first waist region 56 or in both the first
waist region 56 and the second waist region 58. The elastic side panel
members 90 preferably comprise the elastomeric adhesive foam of the
present invention.
While the elasticized side panels 30 may be constructed in a number of
configurations, examples of diapers with elasticized side panels
positioned in the ears (ear flaps) or the diaper are disclosed in U.S.
Pat. No. 4,857,067, entitled "Disposable Diaper Having Shirred Ears"
issued to Wood, et al. on Aug. 15, 1989; U.S. Pat. No. 4,381,781, issued
to Sciaraffa., et al. on May 3, 1983; U.S. Pat. No. 4,938,753, issued to
Van Gompel, et al. on Jul. 3, 1990; and the hereinbefore referenced U.S.
Pat. No. 5,151,092, issued to Buell et al. on Sep. 29, 1992; each of which
are incorporated herein by reference. Thus, the elasticized side panels 30
of the present invention may comprise a separate elastically extensible
material or laminate joined to the diaper. As shown in FIG. 3, each
elasticized side panel 30 preferably comprises an ear flap 88 and an
elastic side panel member 90 operatively associated therewith, such as
described in the above referenced U.S. Pat. No. 5,151,092 issued to Buell,
et al., on Sep. 29, 1992.
As shown in FIG. 3, each ear flap 88 comprises that portion of the side
panel 72 that extends laterally outwardly from and along the side edge 82
of the absorbent core 28 to the longitudinal edge 62 of the diaper 20. The
ear flap 88 generally extends longitudinally from the end edge 64 or the
diaper 20 to the portion of the longitudinal edge 62 of the diaper 20 that
forms the leg opening (this segment of the longitudinal edge 62 being
designated as leg edge 106). In a preferred embodiment of the present
invention, each ear flap 88 in the second waist region 58 is formed by the
portions of the topsheet 24 and the backsheet 26 that extend beyond the
side edge 82 of the absorbent core 28.
In a preferred embodiment of the present invention, the elastic side panel
members 90 are operatively associated with the diaper 20 in the ear flaps
88, preferably between the topsheet 24 and the backsheet 26, so that the
elastic side panel members 90 allow the elasticized side panels 30 to be
elastically extensible in the lateral direction (laterally elastically
extensible). As used herein, the term "elastically extensible" means a
segment or portion of the diaper that will elongate in at least one
direction (preferably the lateral direction for the side panels and the
waistbands) when tensional forces (typically lateral tensional forces for
the side panels and the waistbands) are applied, and will return to about
its pervious size and configuration when the tensional forces are removed.
Generally, elastomeric materials useful in the present invention will
contractively return to at least about 75% of their original configuration
within about 15 seconds or less, preferably within about 5 seconds or
less, upon stretch and immediate release thereof (i.e., a "snappy"
elastic).
The elastic side panel members 90 can be operatively associated in the ear
flaps 88 in a number of different ways, preferably in any of the ways
described in the above referenced U.S. Pat. No. 5,151,092 issued to Buell,
et al. on Sep. 29, 1992. In an especially preferred embodiment, the
elastic side panel member 90 is operatively associated in the ear flap 88
in the form of a "zero strain" stretch laminate, such as previously
described. Thus, the elastic side panel member 90 is joined to the
topsheet 24, the backsheet 26, or both while the elastic side panel member
90 is in a substantially untensioned condition. The elastic side panel
member 90 comprising the elastomeric adhesive foam is preferably
operatively associated in the ear flap 88 by forming a "zero strain"
laminate of the adhesive foam, backsheet, and topsheet as previously
described. At least a portion of the resultant laminate containing the
elastic side panel member 90 is then subjected to mechanical stretching
sufficient to permanently elongate the topsheet and the backsheet
components (typically nonelastic components) of the laminate. The
composite elastomeric laminate is then allowed to return to its
substantially untensioned condition to form the "zero strain" stretch
laminate. (Alternatively, the elastic side panel member 90 could be
operatively associated in a tensioned condition and then subjected to
mechanical stretching; although this is not as preferred as a "zero
strain" stretch laminate.)
In yet another embodiment, the elastic side panel member 90 may be
operatively associated in an elastically contractible condition as
described herein so that the elastic side panel member 90 gathers or
contracts the ear flap 88. For example, the elastic side panel members 90
can be contractibly affixed in the ear flap 88 by laterally extending the
elastic side panel member 90, joining the elastic side panel member 90 to
either or both the topsheet 24 and the backsheet 26, and allowing the
elastic side panel member 90 to assume its relaxed or contracted
orientation. For such pretensioned laminates, the elastic side panel
member 90 will preferably be a shaped elastomeric adhesive foam of the
present invention, e.g., as formed by a rotary mold.
The elastic side panel members 90 may take on a number of different sizes,
shapes, configurations and materials. For example, the elasticized side
panels 30 may be formed from one or a plurality of elastic side panel
members 90 operatively associated in each ear flap 88, the elastic side
panel members 90 may have varying widths and lengths, or the elastic side
panel members 90 may comprise relatively narrow strands of elastomeric
material or a larger area elastomeric patch. Elastomeric materials which
are especially suitable for use as the elastic side panel member 90
(especially for "zero strain" stretch laminates) have an elongation to
break of at least about 400% and an extension force of about 300 grams per
inch of sample width at 50% extension of its unstrained length. In
addition to the elastomeric adhesive foam of the present invention, other
suitable elastomeric materials for use as the elastic side panel members
90 include crosslinked natural rubber foams, polyurethane foams, "live"
synthetic or natural rubber, other synthetic or natural rubber foams,
elastomeric films (including heat shrinkable elastomeric films),
elastomeric scrim, elastomeric woven or nonwoven webs, elastomeric
composites such as elastomeric nonwoven laminates, or the like. Such
materials may be used in combination with the elastomeric adhesive foam of
the present invention, e.g., in laminate form, as the side panel members
90. An external bonding agent such as those described herein may be
desired in order to operatively associate such materials in the side
panels.
As shown in FIG. 3, the elastic side panel member 90 comprises a patch of
elastomeric material (elastomeric patch, preferably the elastomeric
adhesive foam of the present invention) that preferably extends through a
majority of the length of the car flap 88 in the second waist region 58.
When the diaper is manufactured, the elastomeric patch is preferably
positioned so that it forms not only the elastic side panel member 90 of
one diaper but also the positioning patch 50 in the first waist region 56
of the adjacent diaper. Thus, the elastic side panel member 90 preferably
extends from the end edge 64 of the diaper 20 inward toward the leg edge
106 of the ear flap 88. The length and width of the elastic side panel
members 90 are dictated by the diaper's functional design.
While the elastic side panel member 90 may longitudinally extend through
the entire length of the ear flap 88, it is preferred that the elastic
side panel member 90 extend through only a portion of the length of the
ear flap 88 so as to form an extension panel 110. As shown in FIG. 3, the
extension panel 110, the portion of the elasticized side panel
longitudinally extending from the base edge 108 of the elastic side panel
member 90 to the leg edge 106 of the ear flap 88, has also been
mechanically stretched at least to a degree to be extensible (i.e., the
materials that make up the extension panel 110 have been prestrained or
permanently elongated). While there are a number of ways to prestrain the
extension panel 110 of the elasticized side panels 30, the extension panel
110 is preferably prestrained in the same manner as the mechanical
stretching performed on the "zero strain" stretch laminate portion. While
the extension panel 110 of the elasticized side panels 30 may be formed
from a number of different materials, in the preferred embodiment shown in
FIG. 3, the extension panel 110 is formed from the portions of the
topsheet 24 and the backsheet 26 forming the ear flap 88.
The extension characteristics including the extension forces (i.e., force
of elongation), extension modulus, and available stretch (extension); the
contractive forces; elastic creep; elastic hysteresis; and rate of
contraction of the elasticized side panels 30 are important considerations
in the performance or both the elasticized side panels 30 and the diaper
20. The extension characteristics give the diaperer and wearer the overall
perceived "stretchiness" during use. They also effect the ability of the
diaperer to achieve a suitable degree of application stretch (i.e., for a
"normally" perceived tensioning of the diaper during application, the
total amount of resultant stretch is that desired to achieve/maintain good
conformity of fit). An elasticized side panel with a relatively high
extension modulus can cause red marking on the wearer's skin while a
relatively low extension modulus can cause sagging/slipping on the wearer.
Elasticized side panels having too little available stretch may not
achieve a suitable level of body conformity and may contribute in making
the diaper uncomfortable to wear and hard to don. A diaper having
elasticized side panels with very low contractive forces, or poor elastic
creep or elastic hysteresis may not stay in place on the wearer and may
tend to sag/slip on the wearer resulting in poor fit and containment.
For the elasticized side panels 30 of the present invention, it has been
found that the extension characteristics of extension force and extension
modulus are preferably within defined ranges. The extension force
preferably is greater than or equal to about 250 grams.sub.f. It is
preferred that these extension forces be generated at extensions between
about 0.25 inches (6.25 mm) and about 1.25 inches (31.25 mm). For the most
preferred embodiments, the elasticized side panels preferably have an
extensional force between about 250 grams.sub.f and about 500 grams.sub.f
at an extension of between about 0.25 inches (6.25 mm) and about 0.75
inches (18.75 mm). An extension force test suitable for use herein is
described in detail in the above referenced U.S. Pat. No. 5,151,092 issued
to Buell, et al. on Sep. 29, 1992.
Available stretch measures the maximum amount of material available in the
elasticized side panels to reversibly stretch to conform to the wearer's
body during wear. Thus, the amount of available stretch relates to the
maximum amount of extension that the diaperer has available to fit the
diaper to the wearer. In addition, it relates to the maximum amount of
recoverable extension available for the diaper to conform to the wearer's
body. The available stretch is calculated from the equation: ((stretched
length-original length)-original length).times.100. The minimum amount of
available stretch required for a diaper application using elasticized side
panels is preferably an available stretch of at least about 35% for medium
sized diapers and at least about 50% for large sized diapers.
The amount of sustainable contractive force (tension) exerted by the
elasticized side panel 30 on the wearer is an important property of the
elasticized side panel. An elasticized side panel with insufficient
contractive forces may result in the diaper slipping down after being worn
and loaded. Excessive contractive forces may reduce the comfort for the
wearer and produce pressure markings on the wearer's skin. Contractive
force is measured as the force per unit width produced while relaxing an
elastomeric composite at a particular extension. In preferred embodiments
of the present invention, the contractive force of the elasticized side
panels is preferably at least about 90 grams/inch at 50% extension (a 50%
extension would require the sample to be stretched to 1.5 times its
original length).
Typical elastomeric materials show a hysteresis loop of force in their
stress-strain property. That is, for a given extension, the force
(extension force) required to uniaxially extend the elastomeric material
is greater than the force (contractive force) the elastomeric material
exerts when it is allowed to contract from its pre-extended condition. The
former curve can be referred to as the "load curve" and the latter curve
can be referred to as the "unload curve". The "load" extension force
(extension force) is felt by the diaperer when the elasticized side panel
is stretched to apply the diaper to the wearer. The wearer more nearly
"feels" the "unload" contractive forces (contractive forces) once the
diaper is on. Therefore, the hysteresis loss should not be so great that
the contractive force is low enough to allow sagging/slipping of the
diaper on the wearer.
All elastomeric materials undergoing sustained stress/strain have
diminishing forces with time (i.e., elastic creep). Therefore, it is
desired to make sure this reduction in wearing forces over time doesn't
fall below a minimum for wearing stability. The elastic creep should
therefore be kept at a minimum. In preferred embodiments of the present
invention, the final length of the elastomeric material is not greater
than about 1.2 times the original length under tension for 30 minutes. The
extension forces and available stretch of the elasticized waistband 35 can
be important considerations in the performance of both the elasticized
waistband 35 and the elasticized side panels 30. While the extension
forces of the elasticized waistband 35 may be greater than the extension
forces of the elasticized side panels 30, in a preferred embodiment of the
present invention, the extension forces of the elasticized waistband 35 at
its designed extensions is less than or equal to the extension forces of
each elasticized side panel 30 at its designed extensions. An elasticized
waistband 35 having lower extension forces than that of the elasticized
side panels 30 provides for easy stomach movement without displacing the
diaper on the child. The higher extension force elasticized side panels
allow for small dimensional changes over the hip and under the stomach to
keep the product comfortably in tension on the wearer. This design
provides better fit, less leakage and improved comfort for the wearer
through the reduction of sagging, gapping, rollover and roll-in at the
front of the diaper and overall sliding/slipping of the diaper or diaper
absorbent core on the wearer during use.
The elasticized side panels 30 may also be provided with differential
extensibility along the longitudinal axis when stretched in the lateral
direction. As used herein, the term "differential extensibility" is used
to mean a material having a nonuniform degree of elastic extensional
properties, as measured in the direction of stretching at various points
along an axis oriented substantially perpendicular to the direction of
stretching. This may, for example, include varying the elastic modulus or
available stretch or both of the elastomeric material(s). The differential
extensibility is preferably designed into the elasticized side panels 30
so that the lateral extensibility varies longitudinally through at least a
portion of the elasticized side panel as measured from the end edge 64 of
the diaper 20 to the leg edge 106 of the ear flap 88. In an alternative
embodiment, a degree of reduced lateral extensibility in the portion of
the elasticized side panel adjacent to the end edge 64 of the diaper 20
requires more of the total extension to be assumed by the elasticized
waistband 35 thereby resulting in more localized stretching of the
elasticized waistband 35 and a more compliant abdominal fit.
The differential extensibility can be achieved in a number of different
ways. The elasticized side panels 30 can have multiple combined
elastomeric materials, multiple configurations for the elastomeric
materials, or the extension properties or the elastomeric or other
material or materials making up the elasticized side panel may be
nonuniform, For example. differential extensibility can be achieved in
selected adjacent portions or the elasticized side panel by using
elastomeric materials having varying extension or contractive forces,
modulus, or other inherent properties such that more or less (varying)
lateral extensibility is achieved in one portion of the elasticized side
panel than the adjacent portion. The elastomeric materials may also have
varying lengths, sizes, and shapes that provide differential extensibility
Other ways of varying the properties of materials that form the
elasticized side panels as are known in the an may also be used.
A particularly preferred method and apparatus for imparting a varying
degree of extensibility to a "zero strain" stretch laminate is to pass the
"zero strain" stretch laminate through at least one set of meshing
corrugated rolls, at least one of the corrugated rolls having corrugations
of nonuniform profile along its point or points of contact with the "zero
strain" stretch laminate web. As a result, the portions of the laminate
web passing between the set of rolls are nonuniformly stretched. This, in
turn, produces a "zero strain" stretch laminate which is nonuniformly
elasticized in a direction substantially perpendicular to the nonuniformly
profiled corrugations.
The diaper 20 also comprises a fastening system 36 which forms a side
closure which maintains the first waist region 56 and the second waist
region 58 in an overlapping configuration such that lateral tensions are
maintained around the circumference of the diaper to maintain the diaper
on the wearer. Exemplary fastening systems are disclosed in U.S. Pat. No.
4,846,815, entitled "Disposable Diaper Having An Improved Fastening
Device" issued to Scripps on Jul. 11, 1984; U.S. Pat. No. 4,894,060,
entitled "Disposable Diaper With Improved Hook Fastener Portion" issued to
Nestegard on Jan. 16, 1990; U.S. Pat. No. 4,946,527, entitled
"Pressure-Sensitive Adhesive Fastener And Method of Making Same" issued to
Bartfell on Aug. 7, 1990; U.S. Pat. No. 3,848,594 entitled "Tape Fastening
System for Disposable Diaper" issued to Buell on Nov. 19, 1974; U.S. Pat.
No. B1 4,662,875, entitled "Absorbent Article" issued to Hirotsu et at. on
May 5, 1987; and the hereinbefore referenced U.S. Pat. No. 5,151,092,
issued to Buell et al. on Sep. 29, 1992 ; each of which is incorporated
herein by reference. In a preferred embodiment, the fastening system
comprises a dual tension fastening system as described in the U.S. Pat.
No. 5,151,092.
The diaper 20 is preferably applied to a wearer by positioning one of the
waist regions, preferably the second waist region 58, under the wearer's
back and drawing the remainder of the diaper between the wearer's legs so
that the other waist region, preferably the first waist region 56, is
positioned across the front of the wearer. The tape tabs of the fastening
system are then released from the release portion. The diaperer then wraps
the elasticized side panel around the wearer, while still grasping the tab
portion. The elasticized side panels will typically be extended and
tensioned during this operation so as to conform to the size and shape of
the wearer. The fastening system is secured to the outer surface of the
diaper to effect a side closure.
EXAMPLES
A) Preparation of elastomeric, hot-melt, pressure-sensitive adhesive
compositions
Compositions having the formulas shown in Table I may be prepared in the
following manner:
The oil and stabilizer are placed in a Baker-Perkins type jacketed heavy
duty mixer equipped with rotors and the temperature of the mixture is
raised to about 250.degree. o to 350.degree. F. in order to melt the
ingredients. The mixture is then blanketed with CO.sub.2 at a slow flow
rate. The aromatic modified hydrocarbon resins are then slowly added and
melted at a temperature of from about 250.degree. F. to about 350.degree.
F. The block copolymer is then added to the mixture. The mixture is then
agitated until the copolymer is completely melted. A vacuum is then
applied to remove any entrapped air.
The properties of the adhesive compositions may be tested by the following
methods:
Viscosity: The viscosity of the composition is measured at a temperature of
325.degree. F. using a Brookfield Thermosel, in accordance with ASTM
Method D3236-73.
Elastomeric Retention: This measures the force of recovery exhibited by a
sample of the composition following its elongation during a predetermined
interval of time. Samples of the composition are coated on double-sided
release paper using an Acumeter LH1 coater. The coating of the composition
is approximately 5 mils thick and approximately 1.5 inches (38.1 mm) wide.
The samples to be tested are rewound onto themselves. Following a period
of storage for 24 hours, the samples to be tested are cut, in the machine
direction, to a width of approximately 1 inch (25.4 mm), thereby
eliminating any flaws in the samples which could exist along the edges of
same. Samples are then cut to the appropriate length and placed in an
insiron Series IX Tensile Tester. Each sample is then elongated or pulled
to a distance which represents an elongation equal to 40%, and in a second
series of tests, 80% of its unstressed length, at a rate of 20 inches per
minute (50.8 cm/min.). The samples are held at these distances for a
period &thirty (30 ) seconds. The sample is subjected to 2 holding periods
at each elongation. Following the first holding period, the force of
elongation is removed, thereby permitting the sample to return or retract
toward its original length. The sample is then rested for 1 minute.
Following the period of rest, the force of elongation is again applied for
a second holding period to extend the sample to the same distance at the
same rate of speed, (50.8 cm/min). Measurements of the elastomeric
recovery force exhibited by the sample are taken at the beginning of the
test, at the beginning of the first holding period; at the end of the
second holding period; and at the end of the second cycle. The percent
elastomeric retention is calculated by the following formula:
(force exerted by the sample at the end of the second holding
period)/(force exerted at the beginning of the first holding
period)!.times.100=% elastomeric retention
Rate of Recovery: The rate or recovery is measured using a RDA 700
(Rheometrics, Inc.) rheometer in a stress relaxation test mode. The sample
to be tested is positioned between opposing plates of the rheometer and
one of the plates is rotated 180.degree. o relative to the other,
stationary plate. This rotation represents a 50% rotation deformation or
the sample. The force of rotation is then released and the residual energy
of the recovering sample is measured, each second, for a 60 second period
In this particular test, a fully recovered sample is arbitrarily given a
0.01.times.10.sup.3 dynes/cm.sup.2 per second or less recovery rate. The
time required to realize a fully relaxed sample following deformation is
observed. In another test, an initial force is placed on each of the
samples, thereby rotatingly deforming the samples by 50%. For calculation
purposes, a base line stress is taken following a period of 60 seconds of
relaxation. Any stress remaining in the samples following this 60 second
recovery period is considered negligible. The amount or force or residual
energy remaining in the individual samples following this deformation is
then collected during each second, for a period of 60 seconds. Thereafter,
the total energy storage of each of the samples is calculated using the
formula, below:
##EQU1##
Assuming a perfectly elastic sample, the amount of residual energy
remaining in a sample following the release of the deformation force would
be zero. It should be understood, therefore, that as the residual energy
values for each of the samples near zero, the elastic recovery properties
of the samples improves.
The resulting compositions would have the properties given in Table I. The
properties of Comparative Examples 1 (Finalley 198-338) and 2 (based on
the teaching of above referenced patents issued to Bunnelle) are also
shown in Table I. As shown in Table I, the viscosity of the composition
decreases with an increase in styrene content of the copolymer. Table I
also shows that, the higher the styrene content, the faster the
elastomeric recovery rate and the lower the residual energy.
TABLE I
__________________________________________________________________________
Comparative
Comparative
Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ex. 5
Ex. 1 Ex. 2
__________________________________________________________________________
COMPONENT
Vector 4111 45 -- -- -- --
Vector 4211 -- 45 -- 45 45
Vector 4411 -- -- 45 -- --
ECR 165A 40 -- -- -- --
ECR 165C -- 40 -- -- 40
Zonatac Lite 105
-- -- 40 40 --
Kaydol 15 15 15 15
Witco Plastics Oil 380
-- -- -- -- 15
Mark 273 0.5 0.5 0.5 -- 0.5
Irganox 1010 0.25
0.25
0.25
0.25
0.25
Cyanox LTDP 0.25
0.25
0.25
0.25
0.25
PROPERTY
Viscosity at 325.degree. F., cP
34,000
23,300
11,125
21,000
25,250
77,000 >10.sup.6
Elastomeric 84.19
89.7
84.7
93.3
90.5
44.76 68.47
retention, %
Recovery rate, sec
11 11 <1 11 11 31 32
Residual energy/60 sec,
5.924
4.591
0.01
4.809
4.804
15.340 18.534
dynes/cm.sup.2 .times. 10.sup.5
Coupling, % 100 100 100 100 100 80 --
__________________________________________________________________________
Description of Components:
Vector 4111 -- SI-S block copolymer, Dexco Chemical Co., 17% styrene
Vector 4211 -- SI-S block copolymer, Dexco Chemical Co.. 29% styrene
Vector 4411 -- SI-S block copolymer, Dexco Chemical Co., 44% styrene
ECR 165A -- aromatic modified hydrocarbon resin, Exxon Chemical Co.
ECR 165C -- aromatic modified hydrocarbon resin, Exxon Chemical Co.
Zonatac 105 Lite -- aromatic modified hydrocarbon resin, Arizona Chemical
Co.
Kaydol -- paraffinic/napthenic white processing oil, Witco Chemical Co.
Witco Plastics Oil 380 -- paraffinic/napthenic processing oil, Witco
Chemical Co.
Mark 273 -- stabilizing antioxidant, Witco Chemical Co.
Irganox 1010 -- hindered phenol antioxidant, CibaGeigy Corp.
Cyanox LTDP -- DLTDP antioxidant synergist, American Cyanamid
Tensile Strength: To demonstrate the effect of coupling on tensile strength
and recovery after elongation, the following test was conducted. Five
samples of compositions containing copolymers having various percent
couplings as shown in Table II were formed into 1 inch wide (25.4 mm), 5
mil thick pieces. The less than 100% coupled samples were prepared by
blending a composition based on a substantially 100% coupled copolymer
with conventional diblock copolymers. These individual pieces were then
placed in the Instron machine, noted earlier, and were elongated or pulled
to a distance which represented an elongation equal to 40% (and in later
tests, 80%) of its unstressed length, for a period or 30 seconds, then
relaxed for 60 seconds, and then exposed to the same stress for 30
seconds. Data relative to the force of recovery or the individual samples
were collected at the beginning of each pull and just prior to the end or
each of the 30 second holding cycles. The maximum tensile strength was
then measured at the beginning of the first cycle and the percent recovery
calculated as follows:
##EQU2##
TABLE II
______________________________________
Percent Coupled
S-I-S Percent Recovery
Tensile Maximum
______________________________________
100% 78% 32 grams
90% 73% 27 grams
80% 73% 26 grams
70% 67% 24 grams
60% 64% 21 grams
______________________________________
Examples 1-5 will further have a tensile strength of at least 5 psi at 40%
elongation at 25.degree. C.
The results of the test, noted above, reveals that, as the amount of
diblock increased relative to the total concentration of the block
copolymer, the amount of recovery, as well as tensile strength decreased.
Thus, a decrease in coupling efficiency may effect the present recovery
performance and tensile strength of the foams of the present invention in
nearly direct proportion to the amount of diblock which is present in the
adhesive material making up the foam.
B) Preparation of elastomeric adhesive foams
EXAMPLE 1
An elastomeric adhesive foam may be prepared from the above compositions in
the following manner:
A FoamMix.RTM. disk mixer such as shown and described in the above
referenced U.S. Pat. No. 4,778,631 issued to Cobbs, Jr., et al., FIG. 5,
is used to prepare the foam. The system includes a Model 6000 glue
reciter, a Nordson 9400 Series FoamMix.RTM. unit, a H200 gun fitted with a
shim 0.016" thick and 1.5" wide, and a laminating system such as
previously described. The material unwind roll holds release paper.
The elastomeric adhesive material is supplied to the mixer at a pressure of
800 psi at an average flow rate into the mixer of 17.8 pounds per hour.
Nitrogen gas at a temperature of 70.degree. F. and a pressure of 2000 psi
is added to the elastomeric adhesive material close to the adhesive
material inlet of the disc mixer. The amount of the gas is 56 volume %
(based on standard temperature and pressure), the addition being
controlled via the gas metering valve and the differential pressure valve.
The mixer is operated at about 275 rpm shaft rotation to form a solution
of the gas in the adhesive material. The solution passes through the
mixer, outlet, and connecting line and is dispensed through a dispensing
nozzle. The pressure at the nozzle is 515 psi. The temperature of the
gas/adhesive material solution exiting the mixer is 325.degree. F. (all
temperature controls are set to 325.degree. F.). The overall flow rate of
the solution from the mixer is approximately the same as the adhesive
material flow rate because of the low mass of the gas.
A line speed of 50 ft/min resulting in a solution add on of 0.15 g/in2 is
used. The web temperature leaving the chill roll is 130.degree. F.
The resulting product will be a homogeneous adhesive foam. The foam has a
caliper of 18 mils and a width of 1.5 inches. The nitrogen gas content of
the foam will be about 46%.
EXAMPLE 2
An elastomeric adhesive foam may be prepared from the above compositions in
the following manner:
A FoamMix.RTM. disk mixer such as shown and described in the above
referenced U.S. Pat. No. 4,778,631 issued to Cobbs, Jr., et al., FIG. 5,
is used to prepare the foam. The system includes a Model 6000 glue
reciter, a Nordson 9400 Series FoamMix.RTM. unit, a H-20LBS gun fitted
with a 1.5" slot nozzle having a 0.006" shim and a 0.015" land, and a
laminating system such as previously described. The material unwind roll
holds release paper.
The elastomeric adhesive material is supplied to the mixer at a pressure of
1940 psi at an average flow rate into the mixer of 25.6 pounds per hour.
Nitrogen gas at a temperature of 70.degree. F. and a pressure of 2200 psi
is added to the elastomeric adhesive material close to the adhesive
material inlet of the disc mixer. The amount of the gas is 72 volume %
(based on standard temperature and pressure), the addition being
controlled via the gas metering valve and the is differential pressure
valve. The mixer is operated at about 275 rpm shaft rotation to form a
solution of the gas in the adhesive material. The solution passes through
the mixer, outlet, and connecting line and is dispensed through a
dispensing nozzle. The pressure at the nozzle is 1830 psi. The temperature
of the gas/adhesive material solution exiting the mixer is 375.degree. F.
(all temperature controls are set to 375.degree. F.). The overall flow
rate or the solution from the mixer is approximately the same as the
adhesive material flow rate because of the low mass of the gas.
A line speed of 112 fi/min resulting in a solution add on of 0.085 g/in2 is
used.
The resulting product will be a homogeneous adhesive foam. The foam has a
caliper of 19 mils and a width of 1.5 inches. The nitrogen gas content of
the foam will be about 71%.
While particular embodiments of the present invention have been illustrated
and described, it would be obvious to those skilled in the an that various
other changes and modifications can be made without departing from the
spirit and scope of the invention. It is therefore intended to cover in
the appended claims all such changes and modifications that are within the
scope of this invention.
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